Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the diced onion and bell pepper, and sauté for about 3-4 minutes until softened.
Add the minced garlic to the skillet and cook for an additional 1 minute until fragrant.
Stir in the ground beef, breaking it apart with a spatula. Cook until browned and cooked through, about 6-8 minutes. Drain any excess fat.
Season the beef mixture with cumin, chili powder, salt, and black pepper. Mix well and remove from heat.
In a separate skillet, add 1 tablespoon of olive oil and heat over medium heat. Place one tortilla in the skillet.
Evenly spread a portion of the beef mixture on half of the tortilla, then sprinkle shredded cheddar and Monterey Jack cheese on top. Fold the tortilla in half.
Cook the quesadilla for about 3-4 minutes on one side until golden brown, then carefully flip and cook for an additional 3-4 minutes on the other side, until the cheese is melted.
Remove from the skillet and let sit for a minute before cutting into wedges. Repeat with the remaining tortillas and filling.
Serve warm with sour cream and salsa on the side.