Coat the bottom of a 5 quart slow cooker with cooking spray or use a liner. Add marinara sauce, tomatoes,tomato sauce,spices and sugar. Stir until well mixed. Place chicken breast pieces on top of the sauce mix and cover.
Cook on High for 2 - 3 hours, or Low for 4 - 6 hours, until the chicken has reached 165°F on a meat thermometer inserted at the thickest part of the breast.
When the chicken is done, add the uncooked pasta and 1-1/2 cups water to the slow cooker and stir to cover the pasta with the sauce. Pour the frozen peppers and onion mix on top of the chicken and pasta.
Cook on high for an additional hour or until the pasta is al dente. Check after 30 minutes. Add 1/2 cup more water if the sauce is too thick and needed to complete cooking the pasta.
Serve by scooping pasta on a plate, topping with chicken and peppers and onion, and sprinkling with grated cheese.
Notes - to reduce the sodium, use low-sodium spaghetti sauce and tomatoes, also omit the salt from the recipe and only add salt to taste prior to serving.