Fajitas are fun food. You sit down with a huge plate of chopped veggies and salsa, some warm flour tortillas, and a sizzling frying pan full of chicken or beef, put it together yourself, and eat like a pig. The main problem is that you have to do a fair amount of work ahead of time; it's Southwestern food and the Mexican influence means that there's a lot of work that goes into it.
The big time expense is marination; skirt steak, the cut that gave the dish its name in Spanish, needs marinating (I'll tell you a bit about that at the end). This recipe gets you similar results without going through the difficulty of a long, drawn-out marinade. The key is to use a fairly tender cut; I prefer sirloin tips for this, but shell sirloin or New York strip will do the job as well. (Don't use tenderloin, though; for all the money you spend you get a flavorless, almost mushy steak that isn't much good for anything except Beef Stroganoff and showing how much you get paid.)
Like any stirfry, this recipe goes together all at once in the last five minutes; if you want a sizzling pan of fajita innards make sure you have everything organized before the meat goes in the pan. If you do this right, you can have a sizzling pan of fajitas on the table in a half hour from starting your prep work. Better than a half-day marinade, yes?
Start by taking the steak and tossing it in the lime juice; set aside. Preheat a large frying pan on high heat (cast iron is best; wok, paella, or saute pan will all work as well). Slice pepper and onion into strips; do the same to the beef. When pan is hot, add olive oil and garlic; cook until garlic starts to brown and add beef immediately. Once beef has started to cook, add pepper and onion and cook on high heat until the exuded liquid has started to cook off; add salt and chili powder. Bring to table still in pan, still sizzling. Serve with fixings.
Unfortunately I don't have a recipe for either salsa or pico de gallo, so just find your own or pick a good commercial brand. You'll also want the following:
You can always use chicken instead; boneless chicken breasts can be treated in more or less the same way (though a marinade might be better for flavor), and of course you can do skirt steaks (I recommend a lime/garlic/pepper/olive oil marinade, similar to my Lemon Pepper Chicken marinade); I've also heard of pork being used, but I wouldn't really know what would be appropriate as a seasoning.