Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.
In a large skillet over medium-high heat, add vegetable oil. Sauté onion and garlic until fragrant, about 2 minutes.
Add ground beef to the skillet. Season with chili powder, cumin, salt, and pepper. Cook until browned, breaking it up with a spoon.
Warm tortillas in the microwave for 20 seconds to make them pliable.
Pour 1 cup of enchilada sauce into the bottom of the baking dish.
Spoon about 2 tablespoons of the beef mixture onto each tortilla, then roll up and place seam-side down in the dish.
When all enchiladas are in the dish, pour remaining sauce over the top. Sprinkle with cheddar and Monterey Jack cheese.
Bake for 20 minutes, or until cheese is melted and bubbly. If desired, broil for 1-2 minutes to achieve a golden top.