Place oven rack 4-inch from heat. Preheat broiler to high. Place wire racks in 2 large rimmed baking pans; spray with nonstick spray. Place zucchini, eggplant, and mushroom slices in a single layer on prepared racks in pans. Sprinkle with ¼ teaspoon salt.

Broil vegetables on each pan for 6 to 8 minutes or until vegetables begin to brown, turning halfway through. Place vegetables on paper towels; pat dry and cool. Brush one side of cooled zucchini and eggplant slices with pesto; sprinkle with ¼ teaspoon salt. Set vegetables aside.

Stir together 1½ cups shredded mozzarella, ricotta, and Parmesan cheeses, and remaining ½ teaspoon salt in a medium bowl.

To assemble, spread ¼ cup pasta sauce in bottom of a 4-quart slow cooker. Layer with half each of the onions, mushroom, eggplant, and zucchini. Spread with ¼ cup pasta sauce; top with half of ricotta cheese mixture. Layer with remaining onions, mushrooms, eggplant, zucchini, remaining ½ cup pasta sauce, and ricotta cheese mixture. Top with remaining ½ cup shredded mozzarella and fresh mozzarella slices.

Cover and cook on high for 2½ to 3 hours or low for 4 to 5 hours or until eggplant is tender. *Note: To cook on low heat setting, top with remaining ½ cup shredded mozzarella and fresh mozzarella during the last 1 hour of cooking.

To serve, cut lasagna and place on serving plates. Garnish with cracked black pepper and basil, if desired.