Mix the oat bran and baking powder in a bowl. Add the low-fat quark, egg, and salt, then stir until combined. Let it rest for 10 to 12 minutes.
Cover the bowl with a plate and microwave at 600 to 800 watts for 3 to 4 minutes. Flip the bun over, place it on the plate, and microwave uncovered for 1 minute. Let it cool.
Once cooled, slice the bun in half and toast the halves for 1 to 2 minutes.