Combine water, soy sauce, coconut milk, chile paste, and peanut butter in slow cooker crock. Stir in onion, garlic, ginger, green pepper, and diced chicken. Cook on High until chicken is no longer pink, about 4 hours.
Stir the ramen noodles into the crock; reserve seasoning packets. Cook on High until noodles are soft, 15 to 20 minutes. Season to taste with ramen seasoning packets. Garnish soup with cucumbers, green onions, cilantro, and basil before serving.
