The angle on the green and yellow points is sharper than on the brown and tan ones, so suggestions that it's like doing a lonestar are only going to work if you take that into account. It looks challenging and much easier to paint than to sew! It's very attractive though. I think I'd break it down into 4 matching sections with one green and one brown point in each section. They would be uneven quadrangles, but come together at right angles in the middle. If you leave plenty of extra background around the pieces it will be easier to trim it to a neat square when you're done. I would add the center square as an applique because that's easier than piecing it in.