Giroud struck for last night's 1-0 defeat of Norwich City.
Giroud, who "did everything" to leave Stamford Bridge in January, has now scored four times during Project Restart.
"He is a big character for us and he is scoring important goals at the minute," Lampard said. "Just before lockdown he came in and was part of a couple of big results so that's credit he was due anyway.
"He has never given me a problem, he has always trained brilliantly. His professionalism was always good.
"I told him in January I wanted him to stay and he was fantastic in how he handled that. The way he plays is important for us."