Place the bread in a food processor. Turn on the food processor and let it run until the bread turns into large crumbs (some little chunks are fine). 

In a small bowl, stir together the melted butter, garlic salt, onion powder, and cayenne pepper (if desired). 

Spread the breadcrumbs on a sheet pan and drizzle with the garlic butter mixture. Toss gently with a spatula until the crumbs are coated. 

Bake for 8–10 minutes, stirring halfway through, or until the crumbs are lightly golden brown. 

Store in an airtight container.