I simply took my knife and scored the top of the mushroom before I grilled it. Using my sharpest blade, I drug the knife across the face of the mushroom only allowing it to sink about 1/4 of the way through. I made a "tic-tac-toe" pattern using this method. Then grill as you normally would. I like to put mine on a hot grill for about 5 minutes per side, then move it to indirect heat until I'm ready to serve. To plate the mushroom, fold two ends under towards the center. This will open up the grid and make for a beautiful presentation. Here it is served with cauliflower risotto and little leek onion rings.