Pour the apple cider into a small sauce pan; add a handful of thyme sprigs and simmer over medium-low heat until reduced to a syrup. You should end up with about 1/4 cup of liquid - it will continue to thicken as it cools. (This can be done ahead of time and stored in the refrigerator)
Marinate the salmon by placing it in a bowl and add the soy sauce, avocado oil and garlic. Refrigerate until needed.
Preheat the oven to 450 degrees.
Prepare the brussels sprouts by trimming the stem, removing the outer leaves, and cutting in half.
On a sheet pan, toss the brussels sprouts and diced pancetta with 2 tablespoons of the olive oil, season well with salt and pepper, and turn the brussels sprouts, cut side down. Place in the oven, reduce the heat to 425 degrees, and roast for 12 minutes.
While the brussels sprouts are roasting, peel and cut the apples into a large dice. Toss them with the remaining olive oil, season with salt and pepper, and set aside.
After the 12 minutes are up, remove the sheet pan from the oven and add the apples and toss everything around. Make space for the salmon filets and add them to the pan.
Return the pan to the oven, and roast for about 8 minutes.
Turn the temperature up to broil, and place the sheet pan on the highest rack in your oven and broil for a couple of minutes to let everything get well caramelized (this step is optional).
Remove from the oven and drizzle the entire sheet pan with the cider reduction and sprinkle everything with a generous amount of fresh thyme leaves. ENJOY!