Warm the olive oil in a large skillet over medium-high heat. Cook the sausage slices, turning occasionally, until they develop a golden crust, about 3 to 4 minutes each side.
Transfer the cooked sausage to a plate and cover to keep it warm.
Add butter to the pan and let it melt. Toss in the chopped onion and sauté until it softens, about 5 minutes.
Stir in the minced garlic and cook just until fragrant, about 30 seconds.
Add the chopped cabbage, Cajun seasoning, and season with salt and pepper. Cook, stirring occasionally, until the cabbage softens and wilts, approximately 8 to 10 minutes.
Return the sausage to the pan and let all ingredients heat through for another minute.
Sprinkle with chopped parsley and serve immediately.