Preheat the oven to 400°F and line 2 baking sheets with parchment paper.
Combine all the ingredients except the spaghetti squash and olive oil in a large bowl. Knead together until thoroughly combined.
Use a cookie scoop to portion out mixture and roll into 1½-inch balls.
Place the meatballs on one of the baking sheets and transfer to the oven on the middle rack.
Place the spaghetti squash face side down on the second baking sheet and transfer to the oven on the middle rack as well. If you don't have enough room, place the spaghetti squash on the bottom rack.
Bake the meatballs for 30-40 minutes or until done through.
Bake the spaghetti squash until tender, about 45 minutes.
When the spaghetti squash is done, remove from oven and “shred” the meat with a fork into
the casserole dish. Leave the oven on as you put together the casserole.