How to Make It
Steam the potatoes in 1/2 inch water until tender, 16 to 18 minutes; drain.
Meanwhile, heat 1 tablespoon of the oil in a large nonstick skillet over medium-high heat. Season the salmon with 1/2 teaspoon salt and 1/4 teaspoon pepper. Cook until opaque throughout, 3 to 4 minutes per side.
Cook the rosemary and the remaining 4 tablespoons of oil in a small pot over medium heat until the rosemary begins to sizzle, 1 to 2 minutes. Discard the rosemary. Remove from heat; add the olives and vinegar to the oil.
Serve the fish and potatoes over the romaine, drizzled with the warm dressing.