The Tottenham Hotspur midfielder played 83 minutes as a Sheyi Ojo double, a Dominic Solanke strike and a 40-yard free-kick from captain Ryan Ledson fired Neil Dewsnip's Young Lions to a 4-1 victory over Poland in Gdansk on Monday.
"We changed our system to a diamond, and I was happy to see it work," he told TheFA.com.
Poland 1-4 England
U18 International
Monday 17 November
MOSiR Lechia Gdansk Stadium
"I've played it a few times at Tottenham, but not consistently. It was great as it allowed us to have a lot of possession and get our players on the ball. Obviously it worked.
"We got four goals and it was a good experience and hopefully we can use it more in the future.
"And I missed out on the trip to Italy last time, so it was good coming back into the squad and getting the wins."
Having done so in the first game on Saturday, England bounced back again after falling behind - and Onomah was delighted with the impact his team-mates made, especially Ojo.
We were just trying to get into it and as the first half went on we got into it more," he said. "But then second half we started really brightly, especially with Ryan's goal." he said.
Josh Onomah battles for the ball in Poland
"We maintained that energy and kept going, and got rewarded with goals. Lego's [Ledson] was good - I think he meant it so you've got to give him it."
Onomah added: "Sheyi has been with us towards the end of our U17s campaign and at the start of this year, so I was really happy for him to get his two goals and I hope he can go on to score many more.
"And with Dom, he's used to scoring so I'm just happy he did it again for England."
Although he was thrilled to see his friends get on the scoresheet, Onomah revealed that is an aspect of his own game he is keen to improve.
"I've been working on it in training at Spurs. My finishing in and outside of the box, so hopefully it will come sooner or later."
