Heat the oven to 375°F (190°C), line a baking sheet with parchment paper, and set the salmon on the pan. Drizzle it with olive oil, then season with smoked paprika, salt, and pepper. The surface should be evenly coated with oil and seasoning before it goes into the oven.
Bake the salmon for 16 to 18 minutes, adjusting within that range for the thickness of the filet. Remove it when the center is opaque and the flesh separates easily into flakes with a fork. Let the fish reach room temperature, then break it into large chunks in a mixing bowl and chill for 5 to 10 minutes.
Add the red onion, grated radishes, celery, dill, and chives to the chilled salmon. Scatter the vegetables over the fish instead of stirring right away. This keeps the salmon chunks intact while you prepare the dressing.
Whisk the mayonnaise, lemon zest, lemon juice, Dijon mustard, garlic, salt, and pepper in a small bowl. Stir until the dressing looks creamy and evenly seasoned. The mixture should be thick enough to coat a spoon, not runny.
Pour the dressing over the salmon and vegetables, then fold gently with a spatula. Stop as soon as the flakes are coated and the herbs are distributed. Large salmon pieces should still be easy to spot throughout the salad.
Serve the salad cold from the bowl, tucked into butter lettuce leaves, or spooned into a sandwich or wrap. Keep the finished salad chilled until serving. The flavors become especially bright once the lemon dressing has settled around the fish and herbs.