Brown 1/3 cup diced pancetta in olive oil in a pot over medium-high heat until crisp, 2 to 4 minutes. Add 1 pound sliced red cabbage, 1 sliced red onion, 1/2 teaspoon each fennel seeds and kosher salt and a few grinds of pepper. Cook, stirring, 5 minutes. Add 1 cup water, 2 tablespoons balsamic vinegar and 1 tablespoon sugar. Cover and cook over medium heat, stirring, until tender, 15 minutes. Season with salt and pepper and top with parsley.