Preheat oven to 350 degrees. Melt butter in a skillet. Once butter becomes frothy, add breadcrumbs and stir until crumbs are browned. Remove from heat and let cool. Place mushrooms top down on a foil lined baking sheet. Remove sausage from casing and place in skillet. Brown and crumble sausage until cooked through. Spoon sausage into mushrooms and add diced bell pepper. Top mushrooms with Velveeta cubes and buttered bread crumbs. Bake until cheese is melted, about 5–7 minutes. Remove from oven and garnish with parsley, sprouts, and Anaheim pepper slices, as desired.
Serve warm or chilled.