1. Wash little clams.

2. Put little clams into an ovenproof bowl and add the yakiniku sauce. Cover with the edge-open wrap and microwave on 600W for 3-4minutes(1 and half minute to 2minutes on 1200W) until the shells are open.

3. Garnish with edge cut bannnou-negi onions

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.