Heat olive oil in a skillet over medium heat. Add onion and saute 2 to 3 minutes until softened. Add garlic and cook 30 seconds.
Add ground turkey and cook, breaking it apart, about 5 minutes until browned.
Sprinkle with salt, pepper, chili powder, cumin, paprika, oregano, and cayenne if using. Stir well to coat.
Add tomato sauce and simmer 2 to 3 minutes until slightly thickened. Stir in lime juice and remove from heat.
Warm tortillas in a dry skillet 30 seconds per side, or microwave wrapped in a damp paper towel for 20 seconds.
Fill each tortilla with turkey mixture and top with cheese, lettuce, tomato, sour cream, and salsa. Add avocado and cilantro if desired. Serve immediately.