First, wash the peppers, and slice the mushrooms, onions, pepper and grate the cheese.
Cook a polish sausage in a skillet with some oil and once done, cool and then slice into small circular cuts. Slice the sausage on a meat cutting board so you have numerous coins, you want four servings from those sausage rounds.
Prep Veggies
In the same skillet, add butter to saute the onions, mushrooms and bell pepper. Add salt + pepper and continue to saute until onions are carmalized and mushrooms have shed their water and reduced in size.
Prep the Bread
Cut baguette into portions (4″ long sandwiches) and then halved.
Toast the bread in toaster, on a skillet, or in the oven.
Make the Sandwich
On both sides of the open face sandwich, add a portion of the onion and mushrooms, sprinkle pepper, red pepper flakes, and paprika. Top with rounds of sausage, and portion of the grated cheese.
Place the sandwich on a parchment lined baking sheet, move to 350F oven to melt.
Serve open faced with a quick squirt of catsup on top.
Notes
This is what I would get as street food from Polish vendors in Europe. I found a website so I could verify the ingredients, and, although we have some differences, we are in agreement about the basic structure of this food. The main difference is that the street food I had had sausage and red peppers in it while this recipe does not.