In large sauté pan, warm 2 tablespoons oil over medium heat. Season chicken with salt and pepper. Add chicken to pan and sauté until browned, about 5 minutes. Remove chicken to slow cooker and turn pot on low. In same sauté pan, heat remaining 2 tablespoons oil. Add garlic, mushrooms, pepper slices and onion. Saute until vegetables begin to soften, about 5 – 7 minutes. Add vegetables to slow cooker. Add wine to same pan and deglaze about one minute, stirring up brown bits. Pour wine into slow cooker
Add to slow cooker the tomatoes and juices, capers, currents, basil and parsley. Cook for 6 or 7 hours on low (or 3 hours on high), until chicken and vegetables are very tender and sauce has thickened slightly.