Pierce spaghetti squash halves all over using a fork. Place in a microwave-safe dish and cook in a microwave oven until softened, about 10 minutes.
Meanwhile, heat oil in a saucepan over medium heat and cook onion until soft and translucent, about 4 minutes. Add vegetarian ground beef, tomato sauce, peanut butter, oregano, paprika, thyme, tomato paste, turmeric, salt, and pepper and mix well. Simmer until sauce is heated through and starts to thicken, 5 to 10 minutes.
Shred squash flesh using a fork and distribute among 4 plates. Serve with the sauce.