Heat the butter or oil in a large, roomy skillet over medium-low heat. Add the onion.
Cook, stirring every now and then, for 10 minutes, or until the onions are gently browning and translucent.
Add the tempeh bacon and sauté for 1 minute more.
Add the cabbage, 1 cup vegetable broth, and smoked paprika. Continue cooking the vegetables for 10 minutes, stirring often, or until the onions have darkened and the cabbage is very tender. If the vegetables get at all dry, add a few extra splashes of broth.
While the onions and cabbage caramelize, cook the pasta according to package instructions. When the pasta and vegetables are both ready, drain the pasta, reserving 1 cup of pasta water. Add both the pasta and a half cup the pasta water to the skillet.
Warm all of the ingredients through. Taste, and then add salt, pepper, and/or vinegar to your liking. If the mixture gets a little dry, add some more of the pasta water. Serve the pasta, topping each portion with a tablespoon of chopped parsley, if you like.