Birmingham-born Troy Deeney, a boyhood Blues fan, bagged a brace either side of a solo effort from Ikechi Anya, while Almen Abdi fired home a fourth late on as the Hornets moved up to third in the Championship table.
"It was a very good result, a good performance," Zola said.
"I think there were some spells in the game which we were really good, I rate it one of the best performances considering the (injury) difficulties we had.
"But I do think we've played some better games than this."
Deeney has now scored 13 goals this season and the striker, who is out of contract in the summer, was recently linked with a move to Aston Villa.
"We want to keep him, I believe he wants to stay so we're working on getting him signed," said Zola.
"He's 24 years old and a player who has been improving game by game. I don't see why he can't play at a different level."