Marinate the meat (optional): In a mixing bowl, combine the meat with olive oil, minced garlic, chili powder, cumin, paprika, salt, and pepper. Cover and refrigerate for at least 30 minutes to allow the flavors to meld.
Prepare the vegetables: Slice the bell peppers and onions into thin strips.
Cook the meat: Heat a grill or skillet over medium-high heat. Cook the marinated meat for 3-4 minutes per side, or until cooked to your desired doneness. Remove from heat and let it rest for a few minutes before slicing it thinly against the grain.
Sauté the vegetables: In the same skillet, add a bit more olive oil if needed and sauté the sliced bell peppers and onions until they are tender and slightly caramelized, about 5-6 minutes.
Warm the tortillas: Heat the tortillas in a dry skillet or microwave until they are soft and pliable.
Assemble the fajitas: Fill each tortilla with slices of cooked meat and sautéed vegetables. Top with your favorite toppings such as salsa, guacamole, sour cream, shredded cheese, and chopped cilantro.
Serve and enjoy: Serve the fajitas immediately while they are still hot and sizzling.