Take a butter knife and slide it through the connected hamburger buns until the are disconnected the place them in the microwave for 20 sec. Check on them. If there not thawed then continue to set it at 20 secs and check on them. If you don't check on them or if you put them in too long then they'll get as hard as rocks. Then you'll find yourself making an unwanted trip to the store ;(
The best way to thaw frozen buns is to let the buns to sit at room temperature while they are still in the bag. You can also remove them from the fridge and wrap them in a tin foil and place them in an oven at a temperature of about 250 degrees Celsius for about 20 minutes.
Wrap them in a paper towel (The key is to moisten the paper towel first--not soggy wet, wring it out good) on high for about 12-15 sec. The moisture in the towel will turn to steam and steam your buns.