Heat oil in a large skillet over medium-high heat. Add chicken sausage and cook on each side until browned, about 4-5 minutes total. Chicken sausage does not need to be cooked through. Set aside.
Place sliced peppers, onions, tomatoes, sauce, seasoning, pesto and vinegar in slow cooker. Gently stir to combine. Add your sausages to top of vegetable and sauce mixture. Cover and cook on low for 6-8 hours.