Mix pesto with sour cream, and set aside.
Heat grill to medium, about 185ºC. Cut each mushroom in half. Grill mushrooms 5 minutes with lid closed, turn and grill another 4-5 minutes, until cooked through and starting to brown.
Skewer 2-3 mushrooms and remove from grill.
Serve skewered mushrooms with pesto dip.
Hint: Prepared pesto can be found in the grocery store near the pasta and spaghetti sauce.