Here's a link to a post about the preparation of a vegan soy sausage called Soy Longaniza. Trader Joe's carries a similar product called Soyrizo. Both are great for stuffed peppers or any recipe where you'd use hot ground sausage.
For stuffed peppers, mash some beans and crushed tomatoes with the ground "sausage" after you've blanched the peppers. The sausage is VERY spicy so no extra ingredients are needed, in my opinion.
In fact, this is one of those non-recipes where the balance of flavors is totally up to you. Taste as you go and start with a couple of cups of mashed beans, slowly adding the browned "sausage" bits until your preferred heat level is reached. I've used cheddar here, but monterey jack, muenster, or any cheese you prefer would work, including Daiya cheddar (my favorite vegan cheese), which would make this a fine dish for any vegan you know. The peppers I've used are orange sweet ones, but use poblanos for some extra kick.
Fill the blanched peppers with the mixture and top with cheese. Bake at 400 degrees until the cheese is thoroughly melted and just starts to brown.