Preheat oven to 425°F.
Peel and roughly chop the beets. Place in a cast iron pan or an ovenproof dish, drizzle with olive oil and salt generously. Toss until well coated. Place in the oven and roast for about 15 minutes, until cooked halfway.
While the beets roast, combine honey, soy sauce, mirin, minced garlic and chili flakes in a bowl. Mix well. Place the salmon fillets in a bowl and add the sauce. Toss to coat and set aside. Once the beets hit the 15 minute mark, remove them from the oven and push the beets to the sides of the pan, creating some space for the salmon. Place the marinated fish in the middle and transfer back to the oven. Roast until golden brown and cooked through, about 12–15 minutes.
Once done, place the beets into a small bowl and splash with apple cider vinegar. Toss to coat.
Assemble the plate by adding about 2 cups of mixed greens, half of the roasted beets, goat cheese and walnuts. Drizzle with balsamic vinegar. Place the salmon on top and enjoy!
