Heat oven to 450 degrees F. Spray 3 large baking sheets with nonstick cooking spray. Place the zucchini, summer squash, eggplant and Portobello mushrooms on the baking sheets in a single layer. Brush both sides of the vegetables with the Italian dressing.
Bake at 450 degrees F for 25 to 30 minutes or until vegetables are tender, turning them after 15 minutes. Remove from oven and set oven to broil.
Place the pita halves, cut-side up, on a baking sheet and broil for 30 seconds. Spoon about 1-1/2 tablespoons of marinara sauce over each. Arrange an equal amount of roasted vegetables and cheese ribbons over each pizza. Broil for 1 to 2 minutes, until heated through and cheese melts.
Garnish with basil.