Preheat oven to 375ºF. Arrange mushrooms and onions (thinly sliced) on a baking sheet and roast until tender, about 15-20 min.
Mix hummus with chopped & pitted dates & garlic. Add lemon juice if around.
When shrooms are done, split pitas in half horizontally and warm slightly. Spread a generous amount of hummus mix on top half. Place 1/2 cup arugula on the bottom half. Then 1 mushroom cap (dried w/ paper towel), sliced onion, and roasted red pepper.