Preheat oven to 375℉. Line 12 muffin cups.
In a large bowl, combine the rolled oats, yogurt, and coconut milk. Let stand for 10 minutes.
In a separate bowl, mix together the oat flour, brown sugar, coconut flakes, baking powder, baking soda, and salt.
Place the chopped pineapple in the bowl of a food processor and pulse to roughly puree. Measure out 1 cup, and place in a bowl with the banana, egg, and the coconut oil. Mix well. Add this pineapple-banana-egg mixture to the bowl of rolled oats, yogurt, and coconut milk, and mix well to incorporate. Fold the oat flour-coconut flake mixture into the bowl and combine.
Fill the lined muffin cups about 2/3 high. Bake 16-20 minutes, until golden brown and a toothpick inserted into one comes out clean.