Heat 1 tablespoon oil over medium heat in a medium-sized fry pan to glistening (about 1 minute). Add onions, apples, fennel and mushrooms.
Sprinkle with brown sugar and 1/4 teaspoon smoked salt. Reduce heat to medium-low. Sauté, stirring constantly for about 2 minutes. Cover and simmer about 5 minutes until contents caramelize.
While vegetables cook, prepare trout. Pat Steelhead Trout dry on paper towels. Season both sides with pepper and remaining smoked salt. Heat small fry pan with 1 tablespoon oil over medium-high heat to glistening.
Add trout, skin side down to fry pan. Fry over medium-high heat for 5 minutes. Turn fish over and cover pan. Continue to cook for 1 minute.
Turn off heat and keep covered to allow residual heat to finish cooking fish to 145 degrees. Plate vegetable medley. Top with steelhead trout. Garnish with fronds if desired.