Ingredients:
Slab of meat. I use chuck roast.
Beets. Bigger ones are easier to peel, not so big they're cracked. In winter, make sure the stump isn't too rotted. This is much less of issue in high summer-fall.
Carrots.
Salt, pepper, fresh or granulated garlic or whatever else if you want, a little oil.
Maybe some kind of flavorful liquid if you want.
If your container is not reliably leak-proof, then some pearled barley (sometimes, this is hard to find for some reason. Around here, it's in the kosher section or the "international" section with Irish stuff; also bulk food/health food stores)
Get dutch oven or similar pot/pan pretty hot. Salt and brown the slab o' meat. There will be some liquid in the pan. If there's just a little, you're cool. If there's not enough to cover the bottom of the pan, then add some. Water, broth, wine, beer, whatever. Cover tightly (foil is your friend if you don't have high quality cookware) and stick in a warm oven for a while. I tend to do about three hours at 225 or so with just the meat. Maybe I'm doing it wrong, but it's tasty, so I don't care. This is braising, which is just the bee's knees for cooking beef. When it's getting on towards done, pull it out and toss in a whole bunch of quartered/chunked carrots and beets. I used to use other veggies and have realized that they are superfluous and just dilute the flavors. If it's kinda' dry, add a little more liquid it probably won't be. You don't need a lot of liquid. You are kinda' roasting, kinda' steaming the veggies. If they are completely submerged, they lose some of their awesome texture, which isn't mushy like a potato, but has the same stick-to-the ribs quality.
If you don't want the liquidy version, so add some water or broth and some pearled barley.
Reseal and stick it back in the over. When the veggies are done pull it out of the oven and leave it the hell alone. When it's cooled off a little stick it in the fridge. When it's cool enough to handle or when you get around to it, take the hunk of meat apart and either throw out the big chunks or fat and connective tissues that are now pretty easy to remove, or make your dog very happy. If you want, and it's cold, pull any solidified fat off the top. If you're working outdoors and don't have a weight problem, I'd leave it alone. Tear the meat up into chunk small enough that they will warm through in the microwave. Portion out to lunch containers.
If you used barley, it will not be soupy or stewy, it will be more like a casserole. I think it's better without, personally, but more potential more mess and therefore less portable. If you keep a bowl at work, you can seal soup or stew or braise into a wide-mouth quart mason jar way more effectively that a dinky, leaky plastic lunch container, and more durable. Never seen a mason jar warp yet...
This is a little light on straight up carbs for some people's preference. If you want 'em, bread, butter optional, makes a great side, especially if you go to the bakery section of a decent store and get something crusty with a good texture.
It's a pretty long process that involves very little work. I've sung the praises of beets before, but I'm always happy to do it again. Great complement to beef, stands up to cooking better than most vegetables, and obnoxiously healthy. Carrots are good for ya too. Simplicity is good. It's nice only having to buy three things, all of which are main ingredients. nothing piddly and stupid and essential to have to remember. And anyone who says beef isn't healthy hasn't been paying attention to food safety issues. Salads and chicken and lightly cooked or raw stuff, all that pale, rabbit food crap are more prone to becoming seriously toxic if you do the whole cook-on-the-weekends thing or aren't scrupulously careful about keeping the stuff at optimal temperatures and such.
And yeah, this recipe works great with any red meat. I done it with venison and it was great, might try it with bison if I'm ever in a position to obtain an affordable bison roast. Beets stand up well to flavor. For some reason a lot of people find them kind of funky and don't like them. I think it's partly because kids tend not to like strong, earthily flavored vegetables and they are uncommon enough that many people just keep their preconception for life. And I dunno about you, but I was tormented with cold canned pickled beets as a kid.
This is not like that.
ETA: Varies seasonally, of course, but both carrots and beets are often cheaper than potatoes, keep longer than potatoes without getting funky (I refrigerate 'em both), and are less finicky than potatoes to grow your own. And they've got all those vitamins and stuff.