Preheat oven to 400°; pat fish dry, line a sheet pan with foil, drizzle fish with oil, salt + pep; bake 10-12 min until firm, opaque + cooked through, turning pan halfway through cook time

Meanwhile, add potatoes to a large microwave-safe bowl, cover + microwave 3 min; stir potatoes, cover + microwave 2-4 min, then rest 2-3 min; mix in salt/pep, fave spices + 1 tbsp oil

Add spinach + 2-3 tbsp dressing to a large bowl; toss to combine + add to plates

Top salads with potatoes + halibut