Marinate and roast the salmon:
In a food processor, combine the buttermilk, basil, cilantro, scallions, vinegar, honey, ginger, 1 tsp. salt, and 1/8 tsp. pepper. Process until smooth, about 30 seconds. Set aside 3/4 cup for the salad.
Thirty minutes before roasting the salmon, pour the remaining marinade over the salmon in a large rimmed dish and let sit at room temperature. (For the best texture, don't marinate longer than 30 minutes.)
While the salmon is marinating, position a rack in the center of the oven and heat the oven to 400°F. Line a large rimmed baking sheet with foil. When ready to roast the salmon, remove it from the marinade and set on the baking sheet. Bake until just firm to the touch and opaque in the center (use a paring knife to peek), 20 to 25 minutes. Remove from the oven and let rest in the pan for 10 minutes.
Make the salad:
In a medium bowl, mix the cucumbers, onion, olives, cheese, and 1-1/2 tsp. salt. Toss with the reserved buttermilk dressing and season to taste with more salt and pepper.
Use two large spatulas to carefully move the salmon to a platter. Spoon some of the cucumber salad around the salmon and serve the rest in a bowl on the side.
Make Ahead Tips
Prep the cucumber salad up to 3 hours ahead, but do not add the salt or dressing until just before serving.
nutrition information (per serving):
Photo: Scott Phillips