Sauté first 4 ingredients in a large skillet coated with cooking spray over medium-high heat 5 minutes or until onion is tender. Add balsamic vinegar; cook 2 minutes or until liquid is evaporated. Set aside.
Sprinkle cornmeal over baking pan; spread out pizza dough. Bake on bottom oven rack at 425° for 5 minutes.
Stir together pesto and yogurt. Spread over pizza crust, leaving a 1-inch border. Sprinkle with mushroom mixture and fresh basil. Top with mozzarella cheese and tomatoes. Sprinkle with Parmesan cheese.
Bake at 425° on bottom oven rack for 18 minutes or until edges are golden brown and cheese is melted.
*1 (8-ounce) package sliced button mushrooms may be substituted for the portobello mushroom caps.
**1 1/2 cups (6 ounces) shredded part-skim mozzarella cheese may be substituted for fresh mozzarella.