1. Put the mamemoyashi into an ovenproof bowl. Cover with plastic wrap (keeping the edge open), microwave on 600W for 1minute. (30seconds on 1200W) Take the bowl out; evaporate the excess water from the open edge.

2. Put the beef into another ovenproof bowl and add the yakiniku sauce. Mix until the beef is covered with the sauce. Cover with the edge-open wrap and microwave on 600w for 1minute. (30seconds on 1200W)

3. When the beef is cooked, add mamemoyashi and mix. Arrange on plate and serve.

For how long you should cook with your microwave oven, see Cooking Time vs Wattage Conversion.
For more tips of using Microwave Oven, see Sachiko's Guideline to Microwave Cooking.