In a small bowl, combine the olive oil, miso, salt, and mustard. Stir together until well combined and set aside.
Preheat oven to 425°F. Make sure all vegetables are cut and diced to roughly the same size, about ½ inch to ¾ inch. Combine the vegetables on one large sheet pan and the salmon on one small sheet pan. Pour 4 tbsp of the miso mixture over the vegetables and stir until all the vegetables are well coated. Rub the remaining miso mixture on the salmon filets.
Place both the vegetables and the salmon in the preheated oven. Roast the salmon until firm, 6-8 minutes. The USDA recommends cooking to 145°F. Remove from the oven and continue to roast vegetables until they are crisp-tender, 30-40 minutes in total. Remove from oven and let cool while preparing salad.
To serve the salad, place greens on a platter. Season with salt and pepper. Pour half of the dressing (instructions below) over greens and stir to coat. Add prepared vegetables. Flake salmon filets with a fork and add over vegetables. Sprinkle with sunflower seeds and remaining dressing to taste.
For the dressing
In a dressing jar or glass jar with a tight-fitting lid, combine all the ingredients. Shake until the dressing is emulsified, 1 minute. Set aside until ready to use.