Lightly spray the insert of your slow cooker with nonstick cooking spray.
Add the diced onion, red bell pepper, minced garlic, and sliced mushrooms. Stir to combine. (To add more flavor, saute these ingredients in 1 tablespoon of olive oil until the onions are translucent, 5 to 7 minutes.)
1 medium onion, 1 red bell pepper, 4 cloves garlic, 8 ounces sliced mushrooms
Place the chicken breasts on top of the vegetables.
4 boneless skinless chicken breasts
In a separate bowl, whisk together the crushed tomatoes, chicken broth, tomato paste, Italian seasoning, salt, and black pepper until well combined.
28 ounces crushed tomatoes, ½ cup chicken broth, 2 tablespoons tomato paste, 1 tablespoon Italian seasoning, 1 teaspoon salt, ½ teaspoon black pepper
Pour the tomato mixture over the chicken and vegetables in the slow cooker.
Cover the slow cooker and cook on low heat for 6-8 hours or on high heat for 3-4 hours until the chicken is tender and cooked through.
Serve hot, garnished with chopped fresh parsley, if desired.
fresh parsley