Rub spaghetti squash halves insides with 1 tablespoon olive oil and place cut-side down on a baking sheet. Roast spaghetti squash at 400F 35-40 minutes or until spaghetti squash is tender. Cool slightly then shred inside of spaghetti squash into strands and place strands in a large bowl, discarding squash skins. Set spaghetti squash strands aside.

In a medium skillet over medium-high heat, heat remaining 2 tablespoons olive oil. Add onion and garlic to pan, sauteing 2-3 minutes until translucent. Add spinach to pan and let cook a few minutes until wilted. Add spaghetti squash to pan, stirring several minutes until heated through. Season with salt and pepper to taste.

Arrange tomatoes and mozzarella on top of spaghetti squash. Broil under high heat until cheese is browned and melted. Sprinkle top with fresh basil and serve immediately while warm. Enjoy!