Mix the all-purpose seasoning with the ground mustard, salt and 1/4 teaspoon pepper in a small bowl.
Remove core from cabbage and cut into wedges, peel carrots and cut into thirds, rinse potatoes and slice in half. Place veggies into a large bowl and mix with half the seasoning blend and 2 tablespoons of oil. Place on a baking sheet and roast for 25-30 minutes, until tender, stirring once halfway through.
While veggies roast, make a dressing by whisking together 1 tablespoon oil, vinegar, chopped dill, mustard and 1/4 teaspoon pepper. Set aside.
When veggies are approximately 10 minutes from being done, slice steak into two halves, lengthwise; rub with remaining seasoning blend. Heat 1 tablespoon oil in a large skillet over medium-high. Cook each side of steak for 2-3 minutes, or longer if preferred. Place onto cutting board to rest for 5 minutes. Slice against the grain.
Remove veggies from the oven and drizzle with dressing just before serving with steak and sliced oranges on the side.