Evans, who bid £100,000 for the 24-year-old in January when he was at Crawley, had expressed his disappointed with the striker's performance in his first game in charge against Shrewsbury.
But he found his form against the Shrimpers by scoring two goals, the second a 30-yard screamer, to take his tally to 21 goals for the season.
"Lewis can do the most wonderful things. He is a special talented boy that's why Crawley Town and other clubs bid a lot of money for him," Evans said.
"He has got fantastic ability but he has to be working harder and smarter and then his ability will come through.
"I want to keep him here, but if he is not performing he won't be in the team."