In a large bowl, whisk together all Marinade ingredients. Put meat in marinade and set aside for at least one hour.
Preheat oven to 200° F. Set tortillas in for 1 to 3 minutes, to warm. Remove and put into a covered basket.
1 pound beef skirt (flank steak) or chicken breast, sliced into 1/4 x 3-inch long strips
Heat a large skillet and add olive oil. Add marinated meat and onion and sauté until onion becomes translucent. Place cooked meat in a large bowl or platter and serve with tortillas, toppings and garnishes.
For each fajita, fill a tortilla with meat and desired amounts of garnishes and toppings and roll up like a burrito. Serve with refried beans, black beans or Spanish rice.
For spicier marinade, add cayenne pepper or crushed dry red chili pepper. Instead of lime juice, try pineapple juice, papaya juice, beer, wine or barbecue sauce.