Cut spaghetti squash in half and scoop out the seeds. Brush the cut side with olive oil and season with salt and pepper.
Place cut side down in a small dish and bake 50-60 minutes or until tender when poked with a fork.
Combine all meatball ingredients, roll into 24 small meatballs and place on a rimmed baking sheet.
Add meatballs to the oven along with the squash and bake 18-20 minutes or until cooked through and meatballs reach 165°F.
Once squash is tender, scrape the flesh of the squash with a fork to make strands. Toss with butter, season with salt and pepper, then place in the bottom of a baking dish.
Combine pasta sauce and diced tomatoes. Spoon over meatballs.
Top with cheeses and bake 25 minutes or until heated through and bubbly.