Start by removing the stems from the portabello. Brush off any dirt. Place the mushrooms gill side up. Add 1 tablespoon of red pesto in each, distribute it evenly. From the center out to the edge. Now place a pencil-thick slice or two of mozarella in each. Sprinkle some salt on top, and the pine kernels.
Grilling the portabello mushrooms is easy. I usually run my grill at 200° C / 400° F, with the lid on. Simply place the mushrooms on the indirect side and close the lid. Leave them for 10-15 minutes. Don't flip, keep the gill side up at all times.
When the mushrooms are done (the cheese should melt a little), place them on a serving tray/platter with rocket salad and serve immediately.