1.Remove stalks from mushrooms; place, top-side down, on foiled-lined oven tray. Divide pesto into mushroom cups; top each with a tomato half, cut-side up, sprinkle with cheese.
2.Preheat grill (broiler).
3.Grill mushrooms about 5 minutes or until cheese melts.
Prepare the mushrooms ready for grilling the day before; keep covered in the fridge. Mushrooms can be grilled up to 30 minutes before serving.Note