Dariush, 33, is on an impressive seven win streak. The American has not appeared in the octagon since last May, when he defeated Tony Ferguson by unanimous decision.
31-year-old Gamroth has won four fights in a row. On June 25, the Pole defeated Arman Tsarukyan by unanimous decision.
In an interview with ESPN, Darish said the promotion had promised a title shot to the winner of the bout.
Recall that the UFC 280 tournament will head the fight for the vacant lightweight belt between Charles Oliveira and Islam Makhachev.