Preheat the oven to 400ºF.
Half the squash, take out the seeds and place the halved squash on a baking sheet. Put it in the oven and cook for 20 minutes.
1 spaghetti squash
While the squash is baking, add the olive oil and the spinach to a saucepan over medium heat. Cook for 10 minutes. Let it cool, and then put the spinach on a paper towel and press out as much water as possible. Once done, chop into pieces.
1 teaspoon olive oil, 2 cups baby spinach
Add the spinach to a bowl with the ricotta cheese. Mix well.
1½ cups ricotta cheese
Remove the cooked squash from the oven and let it cool. Scrape the insides of the squash with a fork and then place the flesh of the squash into a bowl.
Add 3-5 tablespoons of the spaghetti squash into the bottom, followed by marinara, then the ricotta mixture, and top with the grated cheese. Repeat the steps for a second layer.
2 cups mozzarella cheese, 1½ cups marinara sauce, ¼ cup parmesan cheese, salt and pepper
Place the squash in the broiler until the cheese is melted.