Preheat your oven to 400°F (200°C). Cut the spaghetti squashes in half lengthwise and scoop out the seeds. Drizzle the insides with olive oil and sprinkle with salt, pepper, garlic powder, and onion powder.
Place the squash halves cut-side down on a baking sheet lined with parchment paper. Roast in the preheated oven for 30-40 minutes, or until the flesh is tender and easily shredded with a fork.
Once the squashes are cooked, remove them from the oven and let them cool for a few minutes. Using a fork, scrape the flesh to create spaghetti-like strands and transfer them to a large mixing bowl.
In the bowl with the spaghetti squash, add half of the cheddar cheese, half of the mozzarella cheese, and half of the Parmesan cheese. Mix well to combine.
Transfer the mixture into a greased 9x13-inch baking dish. Top with the remaining cheeses, spreading them evenly over the top.
Return the baking dish to the oven and bake for an additional 15-20 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it cool for a few minutes. Garnish with chopped parsley if desired before serving.