Farrell has made seven changes for the Fiji game with Ulster back row Cormac Izuchukwu and Leinster hooker Gus McCarthy handed their debuts.
"Izzy has been in and around the squad for a while. The first Emerging Ireland tour was when we first came across his ability, his athleticism, his point of difference," observed Farrell.
"That was a couple of years ago but the improvement in his maturity of his game, because he was young in the 15-a-side game when the first tour was on, but the difference between the first and second tour was like chalk and cheese.
"His ability and potential with that maturity, he deserves a shot to show us all what he's got."
On McCarthy, who captained the Ireland Under-20s to a Six Nations Grand Slam in 2023, Farrell said: "He's been a captain and you can see why because his maturity in how he goes about the game."
He added: "We took him on the training week [to Portugal] as a development player and he showed up unbelievably well. He forced our hand to keep him in the squad first and foremost and he deserves a shot to see what he can do as well."