Forest were leading through Andy Reid's early strike when McGugan, who left the City Ground in the summer, curled in a free-kick which Zola the player would have been proud of to secure a 1-1 draw.
"Sometimes it is the way, you can try to do too much against your old team or you can really be up for it, and I thought Lewis was in control," said Zola.
"In the first half he was not at his best but he waited and produced a bit of magic which was welcomed by all of us.
"I see a lot of potential in Lewis. I'm expecting more than that. It's not just about scoring goals, I know he can do that, it'a about being more effective on the pitch and defending as well.
"There were other teams interested in him, he's a quality player, but he was very happy to come here."
Reid opened the scoring with a left-foot thunderbolt in the sixth minute after Marco Cassetti had given the ball away.
But nine minutes after half-time McGugan, who scored 44 goals in seven years in Nottingham, bent the ball around the Forest wall and into the top corner.
Both teams had chances to win it; Forest hit the post twice through Henri Lansbury and, in the final minute, substitute Ishmael Miller while Karl Darlow made fine saves from Sean Murray and Ikechi Anya.
"It was one of those games which was good for the crowd and the TV but certainly not the managers," added Zola. "It was too open. We know we have to defend better than we are at the moment. But if you want to be offensive you can't be perfect at defending, it's a fine line."
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- Andy Reid