- Heat oven to 450°F.
- Line a rimmed baking sheet with parchment paper.
- Arrange mushrooms on a baking sheet, stem sides down, and brush with 1 tablespoon oil.
- Season with salt and pepper.
- Toss tomatoes with remaining oil, garlic, and crushed red pepper flakes and place them on the baking sheet.
- Roast for 25 minutes, turning mushrooms and stirring tomatoes halfway through.
- Transfer tomatoes to a bowl, and toss with reserved juice.
- Heat broiler.
- Toast buns, cut sides up, on a baking sheet for about 45 seconds.
- Broil mushrooms on center rack for 3 minutes.
- Flip, and top 4 buns (bottom half) with cheese, then remaining mushrooms.
- Broil just until cheese melts, about 1 minute.
- Layer tomatoes, arugula, and mushrooms between buns.
Serves 4.
Approximate nutritional information, per serving (not including salt to taste):
310 calories, 11 g fat, 3 g saturated fat, 5 mg cholesterol, 750 mg sodium, 38 g carbohydrate, 6 g fiber, 12 g sugar, 8 g protein