Make the meatballs: In a bowl let the bread soak in the milk for 3 minutes. Add the lamb, garlic, mint, scallion, cinnamon, salt, and pepper, and combine the mixture well. Roll the mixture into 1-inch balls, in a large kettle brown the meatballs over moderate heat for 5 minutes, or until they are just firm to the touch, and transfer them with a slotted spoon to a plate.
Make the sauce: In the kettle cook the onion in the oil over moderately low heat, stirring occasionally and scraping up the brown bits, until it is softened. Add the tomatoes, chopping them with a spoon, and stir in the wine, carrot, garlic, salt and pepper to taste. Bring the liquid to a boil and simmer the mixture, stirring occasionally, for 15 minutes. Add the meatballs and any juices that have accumulated on the plate and simmer the mixture for 5 minutes. Stir in the mint and the Feta and keep the sauce hot over moderately low heat, stirring occasionally.
In a kettle of boiling salted water cook the spaghetti for 8 to 10 minutes, or until it is al dente, and drain it well. Transfer the spaghetti to a heated platter and spoon the sauce over it.