Cannonier hit a hat-trick in victory over Ajax last month.
Lewtas told the club's website: "Getting a hat-trick in Europe isn't easy. I think the real beauty, certainly in terms of Oakley's goals, he's been the one who has finished off the good attacks we have built. His goal against Napoli, he's in the right place at the right time to stick it away, and his finishes against Ajax were excellent. I thought we worked the ball up the pitch really well and created some good opportunities.
"It was an excellent hat-trick and Oakley took his goals really well. I was really pleased for him but also pleased for the team as well because a good striker needs good service, and over the course of the two games I think we've been able to do that for Oakley.
"He scores goals. He is always there to finish, which is the most exciting part of the game. So in fairness to him, he's looked ever so sharp in the two games he has played for us in Europe. We believe if we work the ball into the right areas and create good opportunities, there is nothing better than having someone who you really believe can tuck the ball away. So far Oakley has done that, and the challenge now for him is to continue to finish off the chances and the challenge for the team is to create for him."