Spray a large nonstick skillet with cooking spray. Preheat over high heat.
Add turkey; cook, stirring occasionally, for 5 minutes. Drain fat and discard.
Stir in tomatoes with their juice, green pepper, onion, garlic, oregano, and black pepper. Bring to a boil; reduce heat. Simmer covered for 15 minutes, stirring occasionally. Remove cover; simmer for 15 minutes more. (If you prefer a creamier sauce, give sauce a whirl in your blender or food processor.)
Meanwhile, cook spaghetti in unsalted water. Drain well.
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