Add the ground turkey, onion, Italian seasoning, garlic powder, Parmesan, breadcrumbs, salt, and egg to a large bowl. Mix with a spoon or clean hands until evenly combined. Avoid overmixing or your meatballs can turn tough.

Wet your hands to prevent sticking, then scoop out a heaping tablespoon of mixture at a time and roll into balls. Place on a plate. You should get about 20 to 22 meatballs.

Heat olive oil in a large sauté pan over medium-high heat. Working in batches, cook the meatballs for about 1 minute per side, about 4 minutes total, until browned all around. Transfer to a plate. They won't be fully cooked yet, and that's intentional. They'll finish cooking in the sauce.

In a large saucepan, heat olive oil over medium-high heat. Add the onion and garlic and sauté for 2 minutes until softened and fragrant. Add the carrots and cook for another minute.

Add the diced tomatoes, Italian seasoning, and salt. Stir to combine and bring to a simmer. Cook for 10 minutes, stirring occasionally, until the sauce thickens slightly and the carrots are tender.

Gently nestle the par-cooked meatballs into the sauce. Simmer for another 5 to 6 minutes, until the meatballs are cooked through (internal temperature of 165°F).

While the meatballs finish cooking, bring a large pot of water seasoned with 2 tablespoons of salt to a boil. Add the spaghetti and cook according to package directions until al dente, tender but with a slight bite. Reserve a splash of pasta water before draining in case you need to loosen the sauce.

Drain the spaghetti and return it to the pot. Add the meatballs and sauce and toss everything together. Divide into bowls, top with extra Parmesan, and serve immediately.