In a pan, sweat the onions with the thyme and oregano. Add the chopped garlic, tomato paste, orange zest, and orange juice. Warm through, then add the crushed tomatoes, stewed tomatoes, carrot, sugar, salt & pepper. Simmer for 30 minutes, stirring frequently to prevent burning. Add the cooked meatballs to the sauce and simmer for another 10-15 minutes.