To make slaw, in medium bowl, toss together beet, celery root, green onion, parsley, cider vinegar, and salt. Let rest for at least 30 minutes.
Preheat oven to 300 F. Season trout with salt and pepper and place skin side down on parchment paper-lined baking sheet. Bake fish for 15 minutes, or until just barely cooked through in the thickest part of the flesh. Let rest for 10 minutes and then gently break apart flesh with fork.
In small bowl, stir together yogurt, horseradish, and lemon juice.
Place chunks of trout on tortillas and top with slaw and dollops of horseradish cream.
Recipe Notes
Per serving: 625 calories; 78 g protein; 14 g total fat (3 g sat. fat); 43 g total carbohydrates (13 g sugars, 7 g fiber); 480 mg sodium