09/26/2013 at 03:00 PM EDT
Just a month after welcoming son Axl Jack
showed off her sexy post-baby body on date night with husband
at L.A. hotspot Hakkasan on Wednesday.
The new parents were "laughing and in great spirits," an onlooker tells PEOPLE.
Before indulging in signature dishes like dim sum, roasted silver cod with Champagne, grilled Chilean sea bass with chinese honey, Sanpei corn-fed chicken claypot and macaroons for dessert, Fergie, 38, and Duhamel, 40, took a moment to say grace.
Wearing black skinny jeans and a white blazer, the singer looked "amazing and super fit," the source adds.
The couple recently introduced their bright-eyed boy to the world, sharing a photo
of the infant on Twitter.
– Raha Lewis