Preheat oven to 450 degrees.
Mince garlic, chop bread, peppers, scallion, parsley and spinach. Set aside.
Heat a large skillet on medium heat, and lightly brown bread crumbs, stirring occasionally.
Transfer to a bowl and stir breadcrumbs together with parmesan cheese, vegan parmesan cheese or nutritional yeast, parsley, salt and pepper to taste.
Cut off mushroom stems, chop into ¼ inch pieces and set aside.
Scrape out the gills (black webby stuff) from the mushrooms carefully with a spoon.
Brush mushrooms lightly with oil.
Put whole mushrooms, hollow sides up, on a baking sheet sprayed with cooking spray or covered with parchment paper.
In previously used skillet sauté scallions, garlic, diced peppers and chopped mushroom stems in small amount of oil for 3 minutes, or until half cooked.
Add tomatoes and continue to sauté for 2 minutes.
Add spinach and stir briefly to wilt.
Combine bread crumb mixture with sautéed vegetables and mound onto mushroom centers.
Optional: Top with small amount of finely grated dairy or non-dairy cheese (we used vegan parmesan).
Bake stuffed mushrooms 5 - 7 minutes, then set 6 inches below the broiler.
Broil until stuffing is golden brown, 2 - 5 minutes.
