Heat olive oil in a skillet over medium heat.
Add the chopped onion and sauté until translucent.
Stir in minced garlic and cook for another minute.
Add ground beef, breaking it apart with a spatula.
Cook until the beef is browned and no longer pink.
Mix in chili powder, cumin, salt, and pepper.
Reduce heat and let the mixture simmer for 5 minutes.
Warm the tortillas in a separate pan or microwave.
Spoon the beef mixture onto each tortilla.
Top with diced tomatoes, avocado, lettuce, cheese, and salsa.