Preheat oven to 425 degrees F. Line 15x10x1-inch baking pan with foil. In 12-inch skillet cook and stir sweet pepper, onion, zucchini, carrot, celery, and garlic in hot oil over medium-high heat 4 minutes. Stir in basil, parsley, lemon juice, 1/4 teaspoon each salt and ground black pepper. Top with spinach; cover. Cook for 2 minutes or until spinach is wilted. Remove from heat. Stir crumbs and half of the Parmesan cheese into spinach mixture; set aside.
Remove gills from mushrooms, if desired. Arrange mushrooms, stemmed side up, on prepared pan. Top each with slice of provolone cheese. Divide spinach mixture among mushroom caps. Bake for 15 minutes (mushrooms will water out slightly). Top with remaining Parmesan. Bake 2 minutes more or until heated through. Makes 4 servings.