Slice the plum tomatoes lengthwise. Place in a bowl with carrots and red onion. Toss in olive oil, salt, pepper and garlic. Lay on a sheet tray lined with tin foil. Roast in a pre heated 400°F oven for 45 minutes. Let cool for 15 minutes. Pulse in a food processor until it is a sauce but still chunky. In a dutch oven, saute an onion and another clove of garlic. Add the sauce.and the fresh basil. If you need to thin the sauce add some of the pasta water. Add meatballs and cook for 30 minutes, stirring, a few times. Serve over meatballs and spaghetti. Bon Appetit.