Hi V...I started cutting the loin lengthwise about an inch up from the cutting board, cut into it some and roll it a little, cut some more and roll again, continue until it is somewhat flattened out. Then I had a very lumpy rectangular piece of pork. Covered it with plastic wrap and pounded the lumps flatter. When pounding it out, pull the mallet in the direction you want to help maintain the shape.
Hope this helps, now wishing I had snapped a few pics while cutting it