Preheat oven and pizza stone/steel to 500 degrees for at least 1 hour.
Heat olive oil in a large skillet over medium-high heat.
Add mushrooms and bell peppers, and stirring occasionally, cook until lightly browned, about 8 minutes.
Remove from heat and stir in garlic and season with salt. Set aside until ready to cook the pizza.
Stretch pizza dough into a 12-inch circle onto a piece of parchment paper.
Top with the pizza sauce then 1 ½ cup of the cheese.
Evenly top with cooked mushrooms and bell peppers then olives and red onion. Sprinkle with remaining ¼ cup cheese.
Bake until bubbly and browned, about 12 minutes.
Allow to cool slightly and serve.