Marinate the Beef: Mix olive oil, fajita seasoning, lime juice, garlic, and cumin. Coat the beef with the mixture and let it marinate for at least 30 minutes.
Cook the Vegetables: Sauté the bell peppers and onions in olive oil for 5-7 minutes until tender.
Grill the Beef: Grill the beef for 4-5 minutes per side, then let it rest for a few minutes before slicing thinly.
Assemble the Fajitas: Place beef and sautéed veggies on warmed tortillas. Add toppings like guacamole, salsa, or sour cream.
Serve: Serve immediately with lime wedges. Enjoy!