In a large bowl, toss together the beef slices, sliced onion, sliced bell peppers, olive oil, and fajita seasoning until everything is evenly coated.
Spread the beef and vegetable mixture evenly onto a large baking sheet lined with parchment paper or aluminum foil.
Bake in the preheated oven for about 20-25 minutes, or until the beef is cooked through and the vegetables are tender, stirring halfway through cooking.
While the beef and vegetables are baking, warm the flour tortillas in a skillet or microwave according to package instructions.
Once the beef and vegetables are cooked, remove them from the oven and serve immediately with warmed tortillas and optional toppings.
Notes
Tips for Success
Slice beef against the grain for the most tender result.
Add sliced jalapeños or red pepper flakes if you enjoy more heat.
Use two pans if needed to avoid overcrowding and ensure good caramelization.
How to StoreStore leftover beef and vegetables in an airtight container in the fridge for up to 3 days. Reheat in a skillet or microwave.