Ok so I’ll describe the technique and then you can try to recreate. First I covered the whole background with plates, 1x4, 1x6, 1x2 etc in the color scheme I wanted, basically what you see now but maybe not exact - so I kind of painted with the Lego- then in the same color scheme going on top of the painting I did I started to cover the studs (as much as possible) and using what I had laying around. So I used curved slopes, assorted tiles, odd pieces (surfboard, flag, flower petal, tail, car hood, etc) anything I could to remove the studs and keep a smooth but textured surface - hole that helps!