Preheat the oven broiler. Line a broiler pan with foil.
Broil salmon steaks on the prepared pan 12 minutes, or until easily flaked with a fork.
Heat olive oil in a medium saucepan over medium heat, and saute onion until tender. Stir in garlic, tomatoes, and cilantro. Cook until heated through, 1 to 2 minutes, and remove from heat. Mix in the mangos. Serve over the salmon steaks.