Stir in the tomatoes along with the sugar, breaking up any large pieces with your spoon. Season the mixture with salt and pepper, mixing well to combine. Let the sauce simmer uncovered for approximately 20 minutes, stirring from time to time, until the onion is completely soft and the sauce has reduced to a thick, rich consistency.

While the sauce is simmering, prepare the meatballs: in a large mixing bowl, combine the ground turkey or chicken with the chopped parsley, thyme, grated Parmesan cheese, bread crumbs, and egg. Season generously with salt and pepper. Using your hands, mix everything together until just combined—be careful not to overmix, which can make the meatballs tough. Dampen your hands with water to prevent sticking, then shape the mixture into balls roughly the size of large walnuts, placing them on a plate as you go.

Heat a thin layer of oil in a large frying pan over medium-high heat. Working in batches if necessary to avoid crowding, add the meatballs to the pan and cook for about 8 minutes, turning them occasionally to brown evenly on all sides, until they’re golden and cooked all the way through. Use a slotted spoon to lift the cooked meatballs from the pan and transfer them briefly to paper towels to drain any excess oil. Then nestle the meatballs into the finished tomato sauce and let them heat through gently for about 5 minutes, allowing the flavors to meld together.

Meanwhile, bring a large pot of salted water to a boil and cook the pasta for 8–10 minutes until tender but still with a slight bite. Drain the pasta thoroughly in a colander, then transfer it to serving plates or a large platter. Top the pasta generously with the meatballs and their rich tomato sauce. Finish with a garnish of freshly shredded basil leaves and a sprinkle of grated Parmesan cheese before serving hot.