To garnish: sliced green onion, salsa, sour cream or Greek yogurt, diced avocado, shredded romaine lettuce
Preheat the oven to 400 °F and line a large sheet pan with parchment paper for easier cleanup.
Using a sharp knife, carefully slice each spaghetti squash in half lengthwise and scoop out the seeds. I like to use a grapefruit spoon to make scooping the seeds out easier.
Brush the cut side of each squash half with olive oil, then place them face down on the sheet pan. Roast for 45 minutes, or until the squash strands easily pull away from the rind with a fork.
At the end of roasting, transfer the squash to a large bowl and use a fork to scrape the squash into strands (it's easiest to do one at a time). Place the empty rinds face up on the sheet pan like bowls. Set the cooked squash aside.
Make the spice blend. In a small bowl, mix together the chili powder, cumin, oregano, smoked paprika, onion powder, garlic powder, sea salt and cayenne pepper (if using). Set aside.
Heat a large non-stick skillet over medium heat. Heat 1-2 teaspoons of olive oil, then add the ground turkey. Sauté until almost fully cooked through, then add the green pepper. Continue to cook until the turkey is fully cooked and no longer pink.
Sprinkle in the spice mix and stir until the turkey is evenly covered, then stir in the tomato sauce. Add the reserved spaghetti squash and mix everything together until evenly distributed and warmed through.
Evenly divide the mixture among the four spaghetti squash rinds and top each of them with grated cheese. Roast for another 10 minutes until the cheese is nicely melted.
Serve immediately with your chosen garnishes. Store any leftovers in a sealed container in the refrigerator and eat within 4 days.
See tips in the post for safely slicing spaghetti squash.
A packet of taco seasoning can be used to replace the spice mix. Packaged seasoning varies in salt content, so taste the cooked filling before the final bake and add salt if needed.