Preheat the oven to 400 degrees.
In a large, high sided skillet, warm 2 tablespoons of the olive oil over medium-high heat.
Add the sausage and sear until browned on both sides, for 6 to 8 minutes per side. Use a splatter screen if you have one to limit oil splatters.
Transfer the sausage to a plate; cool slightly.
Add the remaining oil to the skillet.
Add peppers, onion and season with a couple generous pinches of salt.
Sauté, tossing often, scraping the browned bits from the bottom of the pan using the liquids that release from the vegetables, until tender, about 15 minutes.
Add the garlic, season with salt, to taste, and cook for 1 minute.
Meanwhile, remove the skewers from the sausage and cut the outer rings into 3- to 4-inch pieces.
Nestle the sausage into the peppers and onion, add any juices from the plate and bake until the sausage is fully cooked, about 20 minutes.
Serve on a hoagie roll.