Bring a large pot of salted water to a boil and cook the spaghetti until al dente according to package directions, then drain and set aside.
While the pasta cooks, heat a large skillet or Dutch oven over medium heat. Add the ground turkey, Italian sausage, and chopped onion.
Cook the meat and onion, breaking up the meat with a spoon, until browned and the onion is softened, about 6–8 minutes; drain any excess fat or liquid.
Add the tomato sauce, fire-roasted diced tomatoes, Italian-style diced tomatoes, tomato paste, dried Italian seasoning, garlic powder, salt, dried oregano, dried thyme, and dried basil to the pot; stir to combine and bring to a boil.
Reduce heat to low and simmer the sauce, uncovered, for about 20 minutes, stirring occasionally.
Stir in the tablespoon of sugar, taste and adjust seasoning if needed, then toss the sauce with the drained spaghetti or serve the sauce spooned over individual portions.
