Preheat the oven to 400°F. Oil a 12 x 17-inch baking sheet with 2 tablespoons olive oil. Set aside.

Heat a large deep skillet over medium heat. Add 1 tablespoon oil along with the garlic and pepper flakes. Cook, stirring often until fragrant, about 1 minute. Add the spinach and ½ teaspoon salt and cook, stirring often, until the spinach is wilted, another minute. Remove the spinach mixture to a strainer and press firmly to remove any excess liquid. Place the spinach in a medium bowl. Add the ricotta cheese and stir to combine. Set aside.

Using a paper towel, wipe the skillet and bring it back to medium heat. Add the remaining 1 tablespoon oil along with the ground beef and cook, stirring often and breaking apart as needed, until the beef is lightly browned, another 5 minutes. Add the onion, italian seasoning and remaining ½ teaspoon salt and cook until the onion is fragrant and beginning to soften, 3 more minutes. Remove from the heat.

Meanwhile, bring a large pot of salted water to a boil over high heat. Cook the pasta al dente, stirring often to avoid clumping. Drain well, reserving 1 ½ cup of pasta water.

While the pasta is cooking, add the marinara to the pan with the beef and onion and mix well. Add the pasta water, pasta, half the mozzarella and parmesan cheese and stir to combine.

Spread the entire mixture on the prepared 12 x 17-inch baking sheet. Dollop the ricotta-spinach mixture, and sprinkle with remaining shredded cheeses. Bake until the pasta is tender, the sauce is bubbly, and the top is lightly browned, about 30 minutes. Remove from the oven and let rest for 5 minutes before cutting into squares and serving.