In a large nonstick skillet, cook bacon over medium until crisp, 8 minutes. With a slotted spoon, transfer bacon to paper towels to drain. Add 1 tablespoon oil to skillet. Add onion, carrot, celery, and garlic and cook until vegetables are tender, 15 minutes. Transfer to a medium bowl. Add 1 tablespoon oil and turkey to skillet and cook, breaking up meat with a wooden spoon, until almost cooked through, 5 minutes. Add bacon, vegetables, tomatoes, and pinch of red-pepper flakes, if using, to skillet and bring to a simmer; cook until turkey is cooked through and sauce is thickened, 5 minutes. Season with salt and pepper. Serve over spaghetti squash and sprinkle with Parmesan.
Made this for a 4 person dinner party and it was a BIG hit. One of the people didn't like squash (I didn't know this before I made it) but he loved it and went back for seconds. Lots of flavour in the sauce.