01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper. Drizzle the cut sides of the spaghetti squash with 1 tablespoon olive oil and season with salt and black pepper. Arrange the squash halves cut side down on the baking sheet.
02 - Slice the tip off the garlic head to expose the cloves. Drizzle with 1 tablespoon olive oil, wrap tightly in aluminum foil, and place onto the baking sheet alongside the squash.
03 - Transfer squash and garlic to the oven; roast for 35 to 40 minutes until squash is tender and easily separated into strands. Remove both from the oven and let cool slightly.
04 - Lower oven temperature to 375°F. Squeeze roasted garlic cloves into a mixing bowl and mash finely. Add ricotta cheese, egg, grated Parmesan, dried Italian herbs, red pepper flakes, and a pinch of salt and black pepper, then blend until smooth.
05 - Using a fork, gently scrape the spaghetti squash flesh into strands, keeping the outer shells undamaged for stuffing.
06 - Heat a skillet on medium; add zucchini and baby spinach. Sauté for 2 to 3 minutes until softened, then season lightly with salt and black pepper.
07 - Fold the sautéed vegetables and half of the marinara sauce into the ricotta mixture; stir until well combined.
08 - Spoon the ricotta-vegetable mixture into the squash shells. Pour remaining marinara sauce over each and sprinkle with shredded mozzarella cheese.
09 - Arrange the filled squash boats on the baking sheet. Return to oven and bake for 15 to 20 minutes until the cheese is thoroughly melted and begins to bubble.
10 - Remove from oven and garnish each boat with chopped fresh basil before serving.