Heat a large saucepan over medium-low heat. Add the oil and onion and cook the onions to soften but not brown (about 5 minutes). Add the garlic and 1/2 tsp. of the rosemary and cook another minute or until aromatic. Add the basil and tomatoes. Break up the tomatoes. Simmer over low heat for about 20 minutes, stirring from time to time.
While the sauce is simmering, make the meatballs. Combine the turkey, grated garlic, remaining ½ tsp. rosemary and the Parmigiano. Season with 1/4 tsp. salt, and pepper to taste. Mix well and form into 12 meatballs.
When the sauce is done simmering for the 20 minutes, add the meatballs and continue to simmer for 10 minutes, turning the meatballs half way through cooking if they are not completely covered by the sauce.
While the meatballs are simmering, bring a large pot of salted water to a boil. Cook the spaghetti according to package directions. Drain and reserve.
To serve, divide the spaghetti between 4 bowls. Place 3 meatballs in each bowl and then divide the sauce between them.