The Gunners boss made 11 changes to his starting XI ahead of Thursday's Europa LeagueGroup H home meeting with BATE Borisov, opting for players that have seen limited game time this season.
Walcott, who had only made 10 appearances for Arsenal in 2017-18 prior to the clash with the Belarusians, got onto the scoresheet as the hosts ran out 6-0 winners.
"The boss told us to enjoy ourselves," Walcott told BT Sport after the game. "We played with a lot of freedom. Defensively we were solid. Obviously, it's nice to get all these goals.
"There is plenty of competition when you play for Arsenal. We are doing our best to give the manager a headache to pick us for the team. We were very professional tonight. We will see in time what's going to happen."