PREHEAT oven to 450F. Line a baking sheet with foil.
COOK farro, following package directions, until tender. Drain. Reserve 3 cups for Trout Grain Bowl. Toss remaining 2 cups in 2 tsp oil in a bowl.
PLACE trout, skin-side down, on prepared baking sheet. Brush with 2 tsp oil. Sprinkle with 1/2 tsp salt and pepper.
ROAST until a knife tip inserted into the thickest part of fish and gently parting it shows flesh is opaque, about 8 min. Reserve 2 fillets for Trout Grain Bowl.
HEAT remaining 2 tsp oil in a large non-stick frying pan over medium. Add garlic and cook 30 sec. Add chard stems and 1/4 tsp salt. Cook until stems are tender, about 2 min. Add vinegar and chard leaves. Stir until slightly wilted, about 1 min. Serve with trout and farro.