Position the oven rack at the lowest level. If you have a pizza stone, place it in the oven on the rack. Preheat the oven to 425 degrees F.
Heat the oil in a small saucepan and cook the mushrooms and green pepper over medium heat until crisp-tender, about 2 minutes. Cut the crusts into biscuit sized pieces using a biscuit cutter. Distribute the vegetables evenly over the crusts. Reserve 1 cup of the salsa and spoon the remaining salsa evenly over the pizzas. If you don't have a pizza stone, place the pizzas on a baking sheet. They won't be as crisp as they would be if you placed them directly on the rack, but this is a lot less messy.
Bake the pizzas for 10 to 12 minutes, then sprinkle with the cheese. Bake for 7 minutes more. Serve the pizza slices topped with the reserved salsa, olives, cooked ham, shredded lettuce, and sour cream.
For a Greek style pizza, use olives, tapenade, spinach, and feta cheese. For an Italian style pizza, use tomato sauce and provolone cheese.