Coat chicken with flour and pat off the excess. Heat oil in large skillet over medium heat. Add chicken and brown lightly on all sides, 8 to 10 minutes. Remove chicken from the pan and transfer to a 6- to 8-quart slow cooker.
Discard all but 1 tablespoon of oil from the skillet. Add onion and cook, stirring for 1 to 2 minutes. Add mushrooms and cook, stirring for 3 to 4 minutes. Stir in 3 tablespoons of flour. Add reconstituted Kitchen Accomplice Chicken Broth Concentrate or Chicken Bone Broth Concentrate and bring the mixture to a simmer, stirring until it thickens.
Add potatoes to the chicken in the slow cooker, and pour stock mixture over chicken and potatoes. Cover and cook for 3 to 3 1/2 hours on high, or 6 to 6 1/2 hours on low.
Adjust the cooker to high and add spinach and diced roasted red peppers, stirring to combine. Cover and cook about 5-10 minutes more, or until the spinach is wilted. Season to taste with salt and pepper.
