12 medium to large cremini mushrooms, rinsed clean of grit
1 tablespoon olive oil, plus more to grease the grill
1 small yellow bell pepper, diced
1 red jalapeño or red fresno chile pepper, diced (See Recipe Note)
1/2 poblano pepper, diced
1/2 sweet onion, diced
1 cup grated Gruyère cheese
1/2 cup Panko breadcrumbs
Salt and pepper
Preheat a grill to medium-high heat. Use a small paring knife to cut the stem off of each mushroom, then hollow out each mushroom a bit to create a cavity for stuffing. Be careful not to cut through the mushroom.
In a medium skillet, heat a tablespoon of oil over medium heat. Add the diced peppers and onion, and season with a pinch of salt and pepper. Cook the vegetables until they soften, 4 to 5 minutes. Remove the vegetables from the heat and let cool briefly. Stir in the grated cheese.
In a small skillet, toast breadcrumbs over low heat until they are lightly browned.
Stuff mushrooms with the pepper and cheese mixture. Sprinkle breadcrumbs on top of each mushroom.
Lightly oil a paper towel or clean rag with olive oil and brush onto the hot grill. Carefully place the stuffed mushrooms on the hot grill. Cover and let the mushrooms cook for 5 to 6 minutes until the cheese is melted and the mushrooms are just cooked through. Serve while warm.