Heat olive oil in a large, deep skillet or Dutch oven over medium-high heat. Add the sausage rounds and cook, stirring occasionally, until browned on both sides (about 5-7 minutes). Use a slotted spoon to remove the sausage to a plate, leaving the drippings in the pan.
Add the sliced onion to the pan and cook until softened and translucent, about 5-7 minutes.
Add butter to the pan with the onions. When the butter melts, stir in the sliced cabbage and toss with the butter and onions to coat.
Stir in broth, salt, garlic powder, and pepper. Reduce heat to low, cover with a lid, and cook for about 15 minutes, stirring halfway through.
When the cabbage is tender, add the browned sausage back to the pan. Cook and stir until warmed through, about 1 more minute. Garnish with fresh parsley just before serving.