Preheat oven to 450°F. Toss mushrooms with oil and salt; spread on a sheet and in a single layer and lightly coat with Pam cooking spray. Roast until veggies are crispy, about 12 to 15 min; remove from oven and set aside.
Heat an outdoor grill or a grill pan over med high heat. To make pizzas, spread 2 tablespoons of sauce on each tortilla; sprinkle each with 1/4 oregano. Top each with 1 slice of cheese that has been torn into pieces, 1 teaspoon of parmesan and 1/4 of veggies.
Place pizzas on a grill pan and cook till edges begin to brown about 3 to 4 min; rotate pizza. Continue cooking until cheese is bubbly about 2 to 3 min more.