Fajitas are a super easy option. Just slice the LB into thin strips. Get a couple of bell peppers, esp great if one is red, and an onion, and slice those into long thin strips. I usually microwave these for a minute or two on high. You can then add any seasoning you like, maybe one of those packs of fajita seasoning or you can just skip it and bring the seasoning in through other things. Have some spanish/mexican rice on hand - if nothing else use the liquid from a can of rotel as part of the liquid for your rice, and prepare the rice normally. Save the rotel chunks because you will use them. Sour cream, guacamole (you can just mash up an avocado with some chili powder, garlic, cumin, oregano and lemon juice if you don't want to buy guacamole), some shredded cheese, and salsa or pico de gallo (sp?) along wth flour tortillas round things out. Mix the rotel (sans liquid) with salsa, or if you do it ahead you can mix it with the beef strips to help flavor them). My crew likes cold fajitas, so they would happily eat with-o the next step, but I like it hot.
Heat a cast iron skillet over high head. You can use a reg one if you don't have cast iron. When it is VERY hot, pour in some oil just to lightly cover the bottom, and slide the strips of meat, peppers and onion onto the skillet. The purpose is to caramelize them and heat them through - FAST. Stir them around wth a spatula for maybe a minute or two, and when they are just looking cooked, take them off and serve them. The peppers may be a bit brown on the edges, but not burnt. the onions should be soft and sweet, and the beef should be warm and flavorful. If you mixed the beef with rotel, take it out of the rotel before putting in the pan. As the beef is already cooked, add the rotel to another meal or to your salsa.
Enjoy!!! It sounds like a lot, but the prep goes really fast. If you have a good mexican restaurant nearby, ask to buy a couple dozen flour tortillas. Homemade is WAY better than the cardboard sold as tortillas at the grocery. We used to get them at Don Pablos but there are none in our area any more.