1. Bring a large pot of salted water up to boil for the pasta. Heat the oil in a skillet with lid, over medium-high heat. Add the onion, celery, and red pepper and cook, stirring often, until soft, 3 to 4 minutes. Add the garlic and cook 1 minute longer. Transfer half of the vegetables to a large bowl.
2. Add the tomatoes to the skillet and bring to a boil over high heat. Reduce the heat to medium-low and cook, stirring often, until thick and pulpy, 5 to 7 minutes. Season with salt and pepper. Transfer to a food processor and process until smooth (or use an immersion blender to puree). Return sauce to the pan. You should have about a quart of sauce.
3. Meanwhile, add the turkey, spinach, oatmeal, and parmesan to vegetables. Season with 1/2 teaspoon salt, 1/4 teaspoon pepper, and 2 dashes Worcestershire. Mix well and form into 12 large meatballs. (The meatballs can be made several hours in advance and kept covered in the refrigerator). Add the meatballs the sauce, cover and cook, turning once or twice, until meatballs are firm to the touch, about 10 minutes.
4. Cook pasta until al dente, about 12 minutes. Drain well and mix the pasta with about a third of the sauce. Divide evenly among 4 serving bowls and top with meatballs and additional sauce. Serve with grated Parmesan on top.
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