Easy peasy is a popular expression meaning exactly that: “very easy”. According to Urban Dictionary, it was originally used in a 1970’s TV commercial for a detergent called Lemon Squeezy. This is what the mentioned dictionary has to say about it:
… They were with a little girl who points out dirty greasy dishes to an adult (mom or relative) and then this adult produces Lemon Squeezy and they clean the dishes quickly. At the end of the commercial the girl says “Easy Peasy Lemon Squeezy”.
Today it is a silly way to state something was or will be very easy.
JOHN: Aw, come on! This Maths problem is terrible.
PHIL: It isn’t! Let me help you. Mmmmm, you see? Easy peasy!
JOHN: Wow, Phil, thanks, guy!
In this other example from the movie In the Loop, a man mistakes the expression because he has never heard about it before and misuses it in a hilarious way: