Broiled mushrooms make for a ridiculously rich burger and a great substitute for meat when you’re craving that savory taste and meaty texture. Mushrooms are also rich in vitamins and minerals like selenium, an... important antioxidant for metabolic health. If on a low-fiber diet, see the Chef Tips to adapt this dish for your needs.
Preheat the broiler. Make the basil pesto as outlined here.
On a baking sheet, spread the mushroom caps, rounded side down, and the tomatoes, cut side up. Drizzle with olive oil, salt, and pepper.
Place the baking sheet about 6 inches under the broiler for 7 minutes. Next, place the cheese on the mushroom caps and continue to broil until melted, about 2 minutes. Remove from the oven, then lightly toast the burger buns under the broiler.
Lay the buns open on a work surface and spread a heaping tablespoon of Basil Pestoon the bottom side of the buns. Evenly divide the tomatoes between the four buns and place the mushrooms on them, cheesy side down. Top with arugula and the top bun. Serve.
It’s important to buy mushrooms that are fresh. The gills of fresh portobellos should be dry and a light brown color — they are edible so there’s no need to trim them off. If the mushrooms are black and bruised-looking, they’re old.
If possible, avoid buying pre-packed portobello mushroom caps. It’s important to see the color of the gills underneath, and with the way they’re usually packaged, it’s impossible to know what you’ve bought until you get them home.
If on a low-fiber diet:
Use a brioche bun or other soft, white-flour burger bun,