In a shallow dish, coat the chicken breasts evenly with flour, shaking off any excess.
Place the flour-coated chicken in the slow cooker.
Pour the diced tomatoes (with their juices) over the chicken.
Scatter the sliced onions and minced garlic over the chicken and tomatoes.
Sprinkle Italian seasoning, salt, and pepper over everything in the slow cooker.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the chicken is cooked through and tender.
Once done, taste and adjust seasoning if needed.
Serve the chicken with the tomato and onion sauce spooned over the top.
Garnish with chopped fresh parsley if desired.
Enjoy
