For this easy appetizer, mushrooms are stuffed with a mixture of finely chopped bread, goat cheese, scallions, and pepper. Once the mushrooms are filled, they are baked until warm, then broiled to brown the grated cheese on top.
Pulse the bread in the bowl of a food processor until finely chopped. Transfer to a bowl. Place the scallions, bell pepper, and goat cheese in the bowl of a food processor, and pulse until finely chopped and well combined. Transfer mixture to the bowl with the breadcrumbs, and stir. Stir in the cilantro, half the grated Monterey Jack, salt, and pepper.
Heat oven to 350 degrees; position rack in the center of oven. Place mushroom caps, cups facing upward, on a large cookie sheet. Spoon a heaping teaspoon of stuffing mixture into each cap. Bake until mushrooms are tender and filling is hot, 15 to 20 minutes. Remove mushrooms, turn oven to broil, and position rack about 4 inches from broiler. Sprinkle mushrooms with remaining grated cheese, and broil until cheese is golden, about 1 minute. Serve immediately.
The stuffing in Step 1 can be made up to a day ahead and stored in an airtight container in the refrigerator.