Preheat oven to 450 degrees.
In a large bowl, place kale, Brussels sprouts, 2 tablespoons of olive oil, salt, and pepper; toss well then transfer mixture to a large baking dish.
Bake vegetables for 6 minutes then remove from oven and arrange salmon fillets on top.
Bake for 10 minutes or until salmon flakes easily when tested with a fork.
In a medium bowl, whisk together remaining ingredients (lemon juice through mustard) along with remaining 4 tablespoons of olive oil; pour mixture over fish and vegetables then serve.