easyI can tell you how to do that - it's easy!
simpleThe recipe is so simple - you just mix all the ingredients together.
a piece of cakeinformalMy last exam was a piece of cake.
plain sailinginformalOnce we reached the main road the trip was plain sailing.
be smooth sailinginformalThe worst is over. It's smooth sailing from here.
with one arm/hand tied behind your backinformalOh, I can do that with one hand tied behind my back!
as easy as pie/anything/falling off a loginformalYou can do it - it's as easy as pie!
user-friendlyThis latest version of the software is much more user-friendly.
foolproofThis recipe for pastry is practically foolproof.
cushyinformalHe has a very cushy job in an office.