Crispy Oven Beef-and-Bean Tostadas

Preheat oven to 400 degrees F (200 degrees C).

Mix garlic salt, onion powder, garlic powder, cumin, and black pepper together in a small bowl.

Heat a large skillet over medium-high heat. Cook and stir beef, onion, and garlic in the hot skillet until browned and crumbly, 5 to 7 minutes; drain and discard grease. Keep warm while preparing tostada shells.