Step 1

Heat the oven to 400ºF. Coat a 9x13-inch baking dish or large 12-inch ovenproof skillet (preferably cast iron) with olive oil.

Step 2

Place 1 (10-ounce) container thawed frozen cut spinach (including any juices), 1 (about 24-ounce) jar marinara sauce, 1 cup long-grain white rice, 3/4 cup water, 1/4 cup of the grated Parmesan cheese, and 1/2 teaspoon kosher salt in the baking dish. Stir until combined and spread into an even layer.

Step 3

Arrange 1 (about 26-ounce) bag frozen meatballs over the rice mixture. Cover the baking dish tightly in aluminum foil. Bake until the rice is tender, 60 to 70 minutes.

Step 4

Switch the oven to broil. Uncover the baking dish. Sprinkle with 2 cups shredded low-moisture mozzarella cheese and the remaining 1/4 cup grated Parmesan. Return to the oven and broil uncovered until the cheeses are melted and starting to brown in spots, 2 to 4 minutes. Top with more grated Parmesan. Garnish with finely chopped fresh parsley leaves and red pepper flakes if desired.