Heat olive oil in a large skillet over medium-high heat.
Add the ground beef and cook, breaking it up as it browns, for about 5–7 minutes.
Drain any excess fat if necessary and season the beef with fajita seasoning, salt, and pepper.
Add the sliced onions and bell peppers to the skillet with the beef.
Stir to combine and cook for another 5–7 minutes until the vegetables are soft and slightly caramelized.
Drizzle lime juice over the beef and veggie mixture and stir to coat everything evenly.
While the beef and veggies cook, warm the tortillas in a dry skillet for 30 seconds on each side or wrap them in a damp paper towel and microwave for 20–30 seconds.
Serve the beef and vegetable mixture in warm tortillas and add your favorite toppings like cheese, sour cream, guacamole, or salsa.