Onana is now in Germany with Belgium's Euros squad.
“Onana has done well on the whole at Everton,” said Mirallas of his compatriot to evertonfc.com. “It is never easy adapting to the Premier League, but he’s played a lot of games and been an important member of the squad.
“I think his potential is huge, and I think when he manages to understand better and utilise his qualities, then he can go on to be one of the best in the middle for club and country.
“He’s obviously helped by his physical attributes. His size and strength make him a real asset defensively in terms of winning lots of individual duels. Everton are very good at set-pieces and he is one of the biggest dangermen from them in those moments.
“I’d say that size also helps him going forward, too. He’s great at driving up the pitch with the ball at his feet, and I actually think he could do that more. Maybe he will as he develops over the next few years. But it's not just his power, I also like his technical ability which can be underrated.
"Onana moves the ball well and has really impressive technique – good touches in tight areas always. In many ways, he has the whole package of what a midfielder needs, like the perfect box-to-box type who can impact the game both going forward, and when defending.
"He is confident, too, and I think you need that to take control of games. I really like this about him.
“I think we will see him go from strength to strength.”