On a quarter-sheet pan, toss kale and cabbage with 1 tbsp oil, and spread in an even layer; season with salt and bake 6 mins. Season salmon with salt, and add to baking sheet. Bake until salmon is cooked through, 8-9 mins.
Meanwhile, whisk together lemon zest and juice, dill, mustard and remaining 2 tbsp oil. Season to taste with salt.
Drizzle salmon and vegetables with dressing before serving.