Slice the beef sausage into 1/2-inch thick rounds.
Slice the bell peppers and red onion into thin strips and mince the garlic cloves.
Heat the olive oil in a large cast-iron skillet over medium-high heat.
Add the sausage rounds to the skillet and sear until browned on both sides, about 5 minutes.
Remove the sausage from the pan and set it aside on a plate.
In the same skillet, add the bell peppers and red onion, sautéing until they are tender-crisp and slightly charred.
Stir in the minced garlic, sea salt, black pepper, dried oregano, and red pepper flakes, cooking for 1 minute until aromatic.
Return the sausage to the skillet and toss everything together to heat through for 2 minutes.
Garnish with chopped fresh parsley and serve immediately.