In a 3 ½ to 4-quart crock pot, combine meat, onion chunks, and bell pepper pieces.
In medium bowl, combine spaghetti sauce, garlic,1/2 teaspoon of salt, oregano, and black pepper; mix and pour over the meat and vegetables.
Cover and cook on low setting for 9 to 10 hours or on high for 4 1/2 to 5 hours.
If using the low setting, turn to high and add the zucchini; stir well. Cover and cook for 15 minutes more. Season to taste with salt and pepper. Serve over hot spaghetti, mashed potatoes or polenta. Sprinkle with cheese.