Last night I made tostadas. Mainly, because they're an inexpensive and fast way to feed my family when 1) I don't feel like cooking and 2) we won't all be eating at the same time.
If you want, you can make these a lot more complicated and longer to make by making your own refried beans and frying your own corn tortillas, but that defeats the whole "fast" part of it.
What you need:
corn tortillas (I buy mine already cooked)
1 can refried beans
your choice of toppings (We like olives, lettuce, tomato, sour cream and salsa for ours.)
You can also add taco meat if you like.
Preheat oven to 350 degrees. Spread beans on corn tortilla and top with shredded cheese. Place in oven until cheese is melted (2-5 minutes). Top with desired toppings.
Spanish rice would make a nice side dish to this.