Preheat your oven to its highest setting for 20 minutes. Prepare the peppers, onions, and garlic and set them aside in a large bowl. Coat the bottom of the cast iron skillet evenly with the extra-virgin olive oil, add the sausage and place the skillet in the oven.

Cook for 4 minutes on high heat, about 450 to 500 °C (850 to 950 °F). Using oven gloves or a folded over kitchen towel, remove the cast iron to a safe surface. Flip and rotate the sausages and return the skillet to the oven for another 4 minutes, aiming for an internal temperature of 70 °C (160 °F). Remove the skillet to a safe surface and set the sausage aside.

Pour the olive oil and rendered fat from the sausage into the bowl of onions, peppers, and garlic. Season with salt and pepper and mix until the oil thoroughly coats everything. Toss the onions and peppers with crushed red pepper and oregano (optional). Put the skillet in the oven.

Cook for 6 minutes, removing the skillet to toss the onions and peppers every minute. Turn off the oven, remove the cast iron, return the sausage to it, then put the skillet back in the oven for up to 3 minutes.

To serve as a sandwich, layer the onions and peppers into an open Italian sub or Portuguese roll sliced lengthwise. Top with sausage the length of the roll (4 links or ¼ of a pinwheel per roll), then finish with more onions and peppers.

Note: For wetter or saucy versions, after cooking the onions and peppers, deglaze the skillet with white wine or add tomato sauce or purée, toss well and return to the oven for 4 minutes.