The Scotland international has scored three goals for the Toffees this term, and the manager has been impressed with the efforts of the forward.
He told the Liverpool Echo: "It is such a joy to watch him. He can adapt to so many positions and he is one of the most intelligent footballers I have ever worked with and he keeps making really good decisions on the pitch which put us into really good positions.
"He missed an open goal on Saturday, but he's scored seven goals in the last 11 league games and that is a phenomenal return for someone who works incredibly hard off the ball and gives his performances for the team.
"He is in the best moment of his career and he is enjoying every second of it."
Everton host Wolfsburg in the Europa League on Thursday.