- Preheat oven to 400° F.
- Drizzle cut sides of spaghetti squash with oil and season with salt, chili powder, cumin. Place cut side down on a large, rimmed baking sheet. Roast until tender, 30-35 minutes. Let cool slightly. Using a fork, break up squash strands.
Meanwhile, make filling:
- In a large skillet over medium heat, heat olive oil. Add onion and cook until soft, about 5 minutes. Stir in garlic and cook until fragrant, about 1 minute more. Add ground beef, breaking up the meat with a wooden spoon. Cook until beef is no longer pink, about 6 minutes. Drain fat.
- Stir in taco seasoning, then season to taste with salt and pepper. Stir in black beans, cherry tomatoes, and corn.
- Fill each spaghetti squash with beef mixture and top with cheeses. Return to oven to melt cheese, 5 minutes.
- Garnish with cilantro and serve.