01 - Preheat oven to 375°F. Lightly grease a 12-cup muffin tin with cooking spray or oil.
02 - Warm tortillas slightly until pliable. Press each tortilla into a muffin cup, folding edges as needed to fit.
03 - In a skillet over medium heat, add olive oil and sauté onions until softened, about 2 minutes. Add garlic and cook 30 seconds more.
04 - Add ground beef and cook, breaking up meat with a spoon, until browned and cooked through. Drain excess fat if needed.
05 - Stir in taco seasoning and tomato sauce. Simmer for 2-3 minutes until thickened slightly. Season with salt and pepper to taste.
06 - Spoon beef mixture evenly into tortilla cups. Top each with a mix of cheddar and Monterey Jack cheese.
07 - Bake for 12-15 minutes, until cheese is melted and bubbly and tortilla edges are crispy and golden.
08 - Remove from oven and let cool in the muffin tin for 5 minutes before removing.
09 - Top with lettuce, tomatoes, sour cream, green onions, olives, and cilantro as desired. Serve warm.