Preheat oven to 400F.
Wash the portobello mushrooms and remove the stems. Lightly salt them and place on a baking sheet lined with parchment paper. If you decide to grill them, place them on a flat grill plate so that the stuffing doesn’t fall through the grill plates.
Chop the tomatoes and drizzle with olive oil and a pinch of salt.
Add a layer of Arugula pesto and spread evenly over the two mushrooms.
Top with the tomato mixture and roast in the oven for 25 minutes.
Remove from the oven and top with the grated cheese. Lower oven to 360F and place back in the oven for 10-15 minutes longer. Remove from oven and let cool slightly. Serve and enjoy.