Hugo Bonneval, another new recruit, and Marcel van der Merwe went over in the first half and Anthony Belleau scored 13 points from the tee to put Toulon 23-7 up at the break, Pierrick Gunther crossing for the visitors.
Ashton stole the show following the interval, intercepting a stray pass from Colin Slade to score his first try and finishing off a slick move on the right six minutes later.
The clinical Ashton also produced a try-saving tackle in an impressive bow in the French top flight, while Bonneval took his points tally to 21 as Toulon hit the ground running.
Florian Nicot scored the other try for a Pau side that were soundly beaten.
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