Step 1

Toss onion and vinegar in a small bowl; let stand at least 1 hour to pickle.

Step 2

Heat oil in a small skillet over medium-high heat. Working in 2 batches, fry capers until opened and crisp, about 30 seconds. Drain on paper towels.

Step 3

Spread toasts with crème fraîche and season with salt and pepper. Top with smoked salmon, drained pickled red onion, fried capers, and chives; drizzle with oil.

Step 4

Do ahead: Onion can be pickled 1 day ahead. Cover and chill.