Chicken and steak fajitas make a satisfying meal wrapped up in warm tortillas. Marinating the meat first ensures the fajitas are bursting with flavor. Marinate in a covered, nonreactive dish -- stainless steel, glass, plastic and ceramic all qualify -- for only a few hours, because fajita meat is thinly sliced. Make sure the chicken and steak pieces are fully submerged.
Salsa contains everything a marinade needs -- an acid, oil, salt and other herbs, spices and aromatics. Use a store-bought salsa for simplicity, or make your own or something similar with chopped tomatoes, chopped tomatillos or tomato juice. Mix in cooking oil and lemon or lime juice and zest, cilantro, basil, minced garlic, chopped onion and bell pepper, jalapeno or chipotle pepper and cayenne pepper flakes.
Use soy sauce as the base for a saltier steak and chicken fajita marinade. Mix it with an equal amount of cooking oil. Add in other flavorings, such as mirin or sake, lemon or lime juice and zest, chili pepper powder, cumin, cilantro, minced garlic or garlic powder, chopped onion and a little sugar or brown sugar to balance the saltiness.