Heat the oven to 400º. Heat the oil in a large skillet over medium heat. Add the onion, garlic and bell peppers and cook them for 3 minutes, stirring often. Add the beef and use a wooden spoon or a spatula to break it up while it cooks, until it is no longer red, about 3 minutes. Stir in 1/2 cup of the salsa, the chili powder (if you like it HOT, feel free to add more), and the salt and pepper. Cook the mixture over low heat, stirring occasionally, for 10 minutes.

Place the tortillas on a plate and cover them with damp paper towels. Microwave them until warm and pliable, about 45 seconds. Top each tortilla with 1/4 cup of the beef mixture, spreading it to an inch from the edges. Sprinkle cheese evenly over the beef.

Roll up the tortillas and place them on a foil-lined baking sheet with the seam sides down. Brush the taquitos lightly with vegetable oil, then bake them until the filling is heated through and the tortillas are lightly browned, about 8 to 12 minutes. Serve them hot with sour cream and/or salsa.