grid within boundary

hello everybody,

I'm quite new to grasshopper and experiencing a (quite banal?) problem. what i want to do is to create a two dimensional grid of a certain step size within a given boundary ( as shown on the image) which should result in a set of polygons to be extrude later.
I thought i could work this out by intersecting those lines and connecting the corresponding points to curves, but this ended in a complete mess :-)
Is there maybe an easier way(built-in command) to achive this result?
thanks for your help!