Slice the tomatoes, green onions and black olives and set them aside.
Brown the ground beef and drain off the excess fat.
Add the taco seasoning to the ground beef and combine well.
Add about 1/4 cup of salsa to the meat mixture and stir again.
Take 4 tostadas and spread a layer of refried beans on each one.
Spread some ground beef mixture on each tostada. (You will have meat left after this step, unless you want super meaty pizzas. Save the leftovers for tacos, nachos or a taco salad.)
Stack a second tostada on each one. Spread another thin layer of refried black beans on the tops of the second tostadas.
Add a thin layer of enchilada sauce to each Mexican pizza and sprinkle with shredded cheese.
Place the stacks on a baking pan and pop them in the broiler and watch them carefully. Remove them as soon as the cheese is melted.
Add tomatoes, green onions and black olives. Top with sour cream and enjoy!
