Preheat oven to 425°F. Grease 2 cookie sheets; sprinkle each with 2 tablespoons brown rice flour.
Divide dough into 4 pieces. Roll out 2 dough pieces on each cookie sheet into 8-inch rounds. Brush each with 3/4 teaspoon olive oil. Prebake in oven 4 to 5 minutes or until bubbling and golden brown. Remove from oven, and set aside to cool.
Meanwhile, in medium sauté pan, heat remaining 2 tablespoons olive oil over medium-high heat, and add mushrooms. Sauté mushrooms until golden brown, 3 to 4 minutes. Add red onion and bell pepper, and cook 2 to 3 minutes. Add squash and zucchini, and cook 2 to 3 minutes, stirring occasionally. Remove from heat.
In small bowl, mix hummus and oregano. Spread onto prebaked pizza crusts; sprinkle with olives. Divide the vegetables evenly among pizzas.
Bake 6 to 8 minutes or until hot; sprinkle with pepperoncini. Cut into fourths, and serve.