Combine ricotta cheese, cream cheese, half of the mozzarella cheese, Parmesan cheese, basil, Italian seasoning, garlic powder, salt, pepper, and egg in a bowl, along with the wilted spinach. Fill each shell and arrange them in rows in the baking dish. Top with remaining sauce and cheese.
15 ounces ricotta cheese, 4 ounces cream cheese, 3 cups shredded mozzarella cheese, 2 Tablespoons fresh basil, 2 teaspoons Italian seasoning, 1/2 teaspoon kosher salt, 1/2 teaspoon pepper, 1 large egg, 1/2 cup freshly grated Parmesan cheese, 1 pound 4 cups fresh spinach, cooked in boiling water for 30 seconds, then transfer to ice water bath, then squeeze out water (optional), 1/2 teaspoon garlic powder