The 20-year-old scored in Monday's 2-1 win over Bournemouth in the FA Cup fourth-round.
Speaking after the game, Nketiah said: "We started really sharp and played some great football. Towards the end they came back into it and the resilience we showed was excellent.
"It came into me, we've been practicing that in training - I made sure I got into the right place.
"It's nice to be back. I had a great experience at Leeds. It's a dream to play for Arsenal and I'm grateful for this opportunity."