If you flew to Welshpool you could indeed walk the 700m to The Compass for lunch. Which is OK but not special.
Or you could get them to call you a taxi and get taken the 2 miles to Powis Castle where the tea rooms do really nice food. Then walk it off with a stroll around the magnificent gardens for a nice day out. Taxi ride will be about a £5 each way.
Cheers
WWW