This is a classic outside of Fenway Park on game day and at countless other public and family events across the Bay State and New England. It's easy, cheap, and a great crowd-pleaser.
The secret to success here is the perfection of each ingredient. The sausages are the star, so they have to be great - cooked through and with crispy skins, the melted fat saved for the important work ahead. The onions and peppers work best cooked separately or serially. Red and green peppers are a great combination but you can do fine with all green peppers or with whatever your garden/CSA share gives you. A proper New England bun is great, but this works well on pasta too.