Dice 1 of the pears and thinly slice the other. Set aside, keeping the two pears separate. (You may choose to slice the second pear right before serving to prevent it from browning overnight.)
Mash the banana with a fork in a large bowl.
Add the oats, chia seeds, cinnamon, ginger, salt, and milk to the bowl and whisk or mix with a fork until evenly incorporated.
Stir in the raisins and the diced pear.
Evenly spoon the mixture into 3 serving-sized containers and top with the sliced pear.
Seal or tightly cover the containers and refrigerate overnight before serving. Consume within 3–5 days.