In a slow cooker, combine milk, water, oats, brown sugar, butter, and salt. Cook on Low, stirring occasionally when possible, until thick and creamy, 7 to 8 hours.
Divide porridge into 4 servings. Top each with pear slices, 1 Tbsp. walnuts, 1 Tbsp. raisins, 1 Tbsp. cream, 1 tsp. chia seeds, 1 tsp. honey, and ¼ tsp. cinnamon.
Make Ahead: Oatmeal (without toppings) can be made 3 days ahead. Store in an airtight container and refrigerate.
