Preheat oven to 375ºF. Coat 12 muffin holes with cooking spray.
In a large mixing bowl, milk, oats, vanilla extract and egg; set aside 5 minutes for oats to soften and then stir in banana.
In a separate bowl, stir together flour, brown sugar, baking powder, baking soda and salt. Stir flour mixture into yogurt mixture to moisten ingredients (do not beat - the dough will be very thick). Reserve 1 tablespoon chips; stir in remaining chips.
Spoon batter by heaping tablespoons into prepared muffin holes; sprinkle each with a few reserved chocolate chips. Bake until golden brown and a tester inserted in center of a muffin comes out clean, about 15 to 18 minutes.