Onuoha told TheFA.com: "It's nice here and the sun is shining - today was about us getting back into the swing of things and was a bit more relaxed, but I'm expecting it to get more focused over the next few days.
"I had a week off after the end of the Premier League season, resting and spending time with my family and girlfriend. We met up with England on Sunday and it's good to be here with the team. Everybody is really excited about the Championship.
"I'm looking forward to it, being away with England for what could be a month - or what we hope is a month. These opportunities don't come along very often, and it's very exciting for players, so I really want us to make the most of it. We all feel we can really achieve something."