Creamy Tomato Chicken Fettuccine

1 pound boneless, skinless chicken breast, cut into 1/2-inch chunks
1 large onion, chopped
2 cans (14 oz) diced tomatoes
2 t oregano
1 t sugar
1 t salt
1 c alfredo sauce
fettuccine noodles, cooked per package directions
mozzarella cheese

Brown chicken and onion in a small amount of oil. Add tomatoes and spices and simmer until chicken is cooked through. Stir in alfredo sauce and heat until warm. Serve over fettuccine noodles and sprinkle with a small amount of mozzarella cheese.