Heat oil in medium nonstick skillet over medium-high heat. Add onion; cook 3 minutes or until tender, stirring occasionally. Add undrained tomatoes; bring to a boil. Cook 2 minutes or until liquid is almost gone, stirring occasionally.
Reduce heat to medium; add fillets and sprinkle with salt. Cook 10 to 12 minutes or until fish flakes easily with fork (145°F), turning once. Drizzle juice over fillets; sprinkle with olives.