Preheat oven to 375°F. Cook rigatoni pasta according to package directions. Drain and transfer to a large bowl.

Heat olive oil in a large nonstick skillet over medium-high. Add zucchini and cook, stirring occasionally, until lightly browned on all sides, about 4 minutes. Stir in baby spinach; cook until wilted, about 1 minute. Sprinkle with black pepper and 1/4 tsp. kosher salt. Transfer to bowl with pasta.

Whisk together sour cream, plain whole-milk Greek yogurt, egg, and 3⁄4 tsp. kosher salt in a medium bowl until well incorporated.

Stir sour cream mixture into pasta mixture until well coated. Add 12 oz. small fresh mozzarella cheese balls and 1 oz. grated Parmesan cheese to pasta mixture; toss to combine. Gently stir in drained, diced tomatoes.

Transfer mixture to a lightly greased (with cooking spray) 9-inch springform pan, and place on a rimmed baking sheet. Bake in preheated oven until set, about 30 minutes. Top with remaining 4 oz. small fresh mozzarella cheese balls and remaining 1 oz. grated Parmesan cheese, and return to oven. Bake until golden brown, about 5 minutes. Remove and let stand 15 minutes. Release side of springform pan, and cut into 8 pieces. Sprinkle with fresh basil leaves.