Peel banana half and mash in a small bowl. (You can reserve the rest of the banana to slice as garnish, if it is not too mushy.)
Scrape mashed banana into a microwave-safe mug, then stir in vegetable oil, milk, brown sugar, flour, baking powder, cinnamon, and salt.
Stir in chocolate chips.
Scrape any batter on the sides of the mug down into the rest of the batter.
Microwave for 80 seconds on high.
Top with banana slices and more chocolate chips, if desired.
