I made these for the first time last night, and they were a big hit with the family and were super easy. The recipe is originally from the Saving Dinner Summer Frugal e-book, but I made some changes.
1 pound lean ground beef
1/2 cup finely chopped onion
2 cloves garlic, pressed
Salt and pepper to taste
1 (6-oz.) can tomato paste
1 (8-oz.) can tomato sauce
1 teaspoon oregano
1/4 teaspoon crushed red pepper flakes (the recipe called for 1/2 teaspoon)
6 whole wheat hamburger buns
12 slices Mozzarella cheese
In a large skillet or Dutch oven, brown ground beef, onion and garlic. Drain off any excess
fat. Season with salt and pepper to taste and add tomato paste, tomato sauce, oregano, and crushed red pepper flakes. Stir, then simmer for about 6 or 7 minutes. While meat is simmering split burger buns in half and place open side up on large cooking sheet or baking tray. Place under hot broiler for just a moment, just until the buns are barely toasted. Spoon some of the pizza filling onto buns-bottoms and tops. Put a slice of Mozzarella cheese immediately on each bun half. We had some extra sliced olives from our salad that we put on top of the cheese for a few of the halves at this step. Don't sandwich bun tops and bottoms back together. Briefly broil sandwiches, just until cheese is thoroughly melted (and slightly browned, if you like that).
A serving is two halves. Not many veggies here, so we served it with a big salad and some carrot sticks. Everyone actually ate dinner! That's a success in my book.