Pan-Roasted Salmon with Fresh Onion and Fennel Salad

extra-virgin olive oil, plus more for drizzling

skinless salmon fillets (preferably wild; each 5 ounces and 1 1/4 inches thick)

very thinly shaved fennel (from 1 bulb)

pea shoots or mache

fresh white onion, very thinly shaved (1/2 to 3/4 cup)

cilantro leaves, plus cilantro sprigs for garnish (optional)

white balsamic vinegar, or white-wine vinegar and a pinch of sugar

Coarse salt

medium golden tomatoes