Line a large broiler-safe rimmed baking sheet with parchment paper, and set the oven to the “broil” setting on high. If you do not have a broiler-safe pan, preheat the oven to 450ºF (232ºC).
Add the sliced bell peppers and onions to a large bowl and toss to combine.
Pour in the olive oil (or avocado oil) and toss to coat the vegetables with the oil.
Add the sliced smoked sausage rounds into the bowl and toss them well to fully combine them with the peppers and onions.
Spread the peppers, onions, and sausage slices out onto the prepared baking sheet in an even layer.
Season with salt and pepper (and/or your favorite seasonings) to your taste (keep in mind that smoked sausage is often salty).
Place the baking sheet in the oven and broil for 10-12 minutes, tossing halfway through the cooking time to encourage even cooking. If you are not using the broil function, bake for 20-25 minutes, or until the sausages are browning well and the onions and peppers are soft.
Remove from the oven and serve immediately with rice, mashed potatoes, or your favorite side dishes.