2) Griddle for 5 minutes on each side, or until the salmon is almost cooked through. Remove to a plate and allow it to rest for 15 minutes.
3) To assemble the sandwiches, slice the rolls in 1/2 crosswise. Spread a tbsp of sauce on each cut side. On the bottom 1/2, place some mesclun salad and then a piece of salmon. Place the top of the roll on the salmon and serve immediately.
For the sauce:
1) Place the mayonnaise, sour cream, vinegar, basil, dill, spring onions, salt and pepper in the bowl of a food processor fitted with a steel blade. Process until combined.
2) Add the capers and pulse 2 or 3 more times.