Make the crust: Generously spray 2 (12-inch) pizza pans with nonstick vegetable oil cooking spray. In a medium bowl, stir together all of the crust ingredients to make a smooth, thick, pancake-like batter. Using a rubber spatula, spread the batter as thin and evenly as possible over the 2 pans.
Place pizza crusts on center racks of the oven and bake for about 12 to 15 minutes, or until lightly golden brown and firm to touch.
Remove crusts from oven and increase the oven temperature to 400 degrees F.
Meanwhile, make the sauce: In a saucepan over medium heat, heat olive oil and then sweat onions and garlic in oil, cooking just until softened and translucent. Add diced tomatoes and the remaining ingredients and simmer for about 2 minutes.
Compile the pizzas: Spread the tomato sauce and then the mozzarella cheese evenly over both crusts. Top 1 pizza with pepperoni, sausage, and ham, and top the other with the bell pepper strips, onions, and mushrooms. Lightly sprinkle 1 tablespoon olive oil over each pizza, and sprinkle each with a dash of dried oregano.
Place the pizzas back in the oven to bake for another 10 to 12 minutes, or until the cheese melts and starts to brown. Cut each pizza into 8 slices.