Heat oil in a 3 quart saucepan until it shimmers. Add onion and reduce heat to medium. Cook until tender, but do not brown. Remove from saucepan and hold. Season chicken with salt and pepper and add to pan. Cover and cook for 15-20 minutes turning once. Cook until chicken pieces are nicely browned on both sides. While cooking chicken, blend chicken stock and peanut butter in blender until smooth. Add garlic and red pepper and blend into a paste. When chicken is browned, add peanut butter mixture to pan and stir. Add onions back into pan. Cover and cook for 10 minutes. Add potatoes, 1 ½ tsp. salt, ¼ tsp. black pepper. Cover pan and cook for 30 minutes or until chicken is fully cooked. Adjust with broth if needed. Add lemon juice and stir in spinach. Stir and continue to cook until spinach is wilted. Serve over white rice.