Despite Plato winning two races from the recent Dunlop British Touring Car Championship action at Snetterton, Onslow-Cole's impressive 6th place finish in race one - from the back of the grid - was deemed worthy of the accolade.
It is the second time this season that Onslow-Cole has won the award following his star turn at Oulton Park earlier in the year.
The Team Aon star said: "To win one award is great, but to win two is just fantastic. I suppose I must be doing something right, even with one or two moans about the car I am in!
"I'd like to thanks everyone who voted, and hope to give them some more moments to cheer in the coming rounds."
Teresa Jones of Bridgnorth, Shropshire, voted for Tom and will present him with his bottle of champagne at this weekend's round of racing at Silverstone.
She said: "HiQ has made my day! I can't believe I've won and I can't wait to meet Tom at Silverstone."
She will also win a bottle of bubbly for herself, a grid walk before one or the races, and a pair of complimentary tickets to a future race.
Tom polled 42 per cent of votes, narrowly beating Jason Plato into second place (37 per cent).
HiQ's marketing manager Geraldine McGovern said: "Results like this are why we set-up these champagne moments back in 2008. It may not be a first place finish, but a brilliant move or display of driving elsewhere on the track."