Smoked Trout with Pea Shoots and Spring Onions

Name: Smoked Trout with Pea Shoots and Spring Onions
Ingredients: ¼ cup crème fraîche or sour cream; 2 tablespoons drained prepared horseradish; Kosher salt and freshly ground black pepper; 4 small purple or white spring onion bulbs, thinly sliced crosswise; 1 tablespoon white wine vinegar; 2 teaspoons vegetable oil; 6 cups pea shoots (tendrils) and/or pea sprouts or watercress leaves with tender stems; 6 oz. smoked trout fillet, skin and any bones removed, broken into large pieces; Edible flowers (for serving; optional)