Cheeseburger Quesadilla on a Sheet Pan

Ingredients
1 tablespoon vegetable oil
1 onion
3 garlic cloves
2 lbs ground beef
1 tablespoon salt
1 tablespoon pepper
1 cup ketchup
12 tortillas
24 slices cheddar cheese
1/2 cup melted butter
1 tablespoon sesame seeds

Method