Cut your choice of meat into strips. It is advisable to slice the meat against the grain to make it less chewy.
In a bowl, mix soy sauce, lemon/lime juice and olive oil. Marinate the meat strips in this sauce for 1-2 hours. Marinate the onions and peppers afterwards or in a separate bowl.
Add the olive oil for cooking to a skillet and heat it until it is hot. When oil is hot enough, it should start to ripple or shimmer.
Add and brown meat strips. When browned, remove from the pan and set aside. Add onions and peppers, sautéing them until soft. Add the meat back into the pan or skillet and heat through.
Serve the meat on tortillas or tacos, and garnish with salsa, cilantro. Guacamole and sour cream also tastes great in fajitas. If you want spicy, hot fajitas, you can add a teaspoon of chili powder to your soy sauce marinade.