Grigg latched on to Toumani Diagouraga's throughball to slot home on the stroke of half-time for his fourth strike of the campaign.
It ensured the Bees registered their eighth win from their last nine games and Rosler was quick to single out his matchwinner.
"Will Grigg was outstanding in my opinion," said Rosler. "He had very good movement throughout the 90 minutes and had quite a few chances for us. I'm very pleased with his contribution.
"Will is back on track in terms of confidence. He has been coming off the bench for us and doing well and I was delighted for him, not just because of the goal but because of his all-round play.
"Notts County were causing us problems down the left with their number seven (Jack Grealish) but on the whole I'm very happy to come away with the points."