1. Preheat oven to 300°.
2. Heat a large ovenproof skillet over medium-high heat. Add oil; swirl to coat. Add kohlrabi to pan; cook 2 minutes or until browned, stirring occasionally. Stir in mustard seeds, salt, and pepper; cook 1 minute. Add 1/2 cup water, honey, vinegar, butter, and onion; bring mixture to a boil.
3. Cover and bake at 300° for 1 hour or until kohlrabi is tender. Uncover and remove kohlrabi from pan; place on a serving platter. Return pan to medium-high heat. Bring to a boil; cook 6 minutes or until syrupy. Drizzle kohlrabi with syrup; sprinkle evenly with chopped parsley.