Tom Watson, who had been scheduled to face Trigg, was forced to withdraw due to a back injury.
Wallhead (21-6), who trains out of Team Rough House with the likes of Dan Hardy, Paul Daley and Ross Pearson, won his Bellator debut in October, but earlier this year had an eight-fight win streak snapped by tournament runner-up Rick Hawn. Prior to Bellator, the judo black belt was a reserve on The Ultimate Fighter 9, but never received the call up.
Trigg (21-8) made his BAMMA debut in May, stopping John Phillips in the first round. Trigg, 39, has won back-to-back fights since his release from the UFC last year.
Also on the BAMMA 7 card are: Leonardo Santos vs. Rob Sinclair, Efrain Escudero vs. Tim Radcliffe and Matt Ewin vs. Valentino Petrescu.