In a small saucepan over medium-high heat, combine the soy sauce, monk fruit, ginger, garlic, vinegar and xanthan gum. Bring to a simmer, stirring until the monk fruit has dissolved, about 1 minute. Let cool to room temperature. Reserve 1/4 cup of the sauce.
Place the salmon fillets in separate ziplock bags and pour the remaining sauce into the bags, dividing evenly. Using the displacement method (submerge most of the bag in water, forcing the air out), remove air and seal the bag. Refrigerate for at least 1 hour or up to 4 hours.
Prepare a sous vide immersion circulator for use according to the manufacturer’s instructions. Preheat the water to 126°F. Place the bags into the circulating water and cook for 30 minutes for medium doneness.
While the fish cooks, prepare the cucumber avocado salad by mixing all ingredients together. Let sit while fish finishes cooking.
Carefully remove the bags from the circulating water. Remove the fish from the bags. If your fish has skin on it, sear to crisp skin.
Spoon the warm sauce over the fish and serve with cucumber and avocado salad.
Notes
You can also slow roast the salmon at 275ºF in the oven for 15-20 minutes instead of cooking it sous vide. Brush with the extra sauce and a bit of oil before placing in the oven.