Place 2-1/2 tablespoons oats, the flour, sugar and cinnamon in microwave-safe mug; stir to mix well. Stir in banana and egg white until well blended, scraping sides and bottom of mug with rubber spatula. Sprinkle with remaining 1-1/2 teaspoons oats.
Microwave on HIGH 80 to 90 seconds until risen and just firm to the touch. Let stand 3 to 5 minutes before serving.