01 - Preheat oven to 425°F. Line a baking tray with parchment paper. Place tomatoes cut side up, onion quarters, and garlic cloves on the tray. Drizzle with 2 tbsp olive oil, then sprinkle with 1 tsp salt, ½ tsp pepper, and 1 tsp dried oregano.
02 - Roast the vegetables for 25 minutes until tomatoes are soft and slightly caramelized.
03 - While vegetables roast, combine breadcrumbs and milk in a large bowl. Let soak for 5 minutes. Add ground turkey, egg, Parmesan, parsley, minced garlic, 1 tsp salt, ½ tsp pepper, and thyme. Mix gently with hands until just combined.
04 - Shape the mixture into 16 golf ball-sized meatballs.
05 - Heat 2 tbsp olive oil in a large skillet over medium heat. Brown meatballs in batches, turning until golden on all sides, about 5 minutes per batch. Transfer to a plate.
06 - Transfer roasted vegetables to a blender or food processor. Add sugar if using. Blend until smooth. Pour sauce into a large, deep skillet or saucepan and bring to a gentle simmer.
07 - Add browned meatballs to the sauce. Cover and simmer on low heat for 15-20 minutes until meatballs are cooked through.
08 - Stir in fresh basil leaves just before serving.