Preheat outdoor or indoor grill or oven broiler.
In a small bowl, combine first 5 ingredients (mayo through dill); set aside. Coat the grill with a little olive oil and grill fish for 3 to 4 minutes per side or until cooked to desired preference.
Combine mixed salad greens and baby spinach and arrange on dinner plates; top each with a fish fillet, then dill sauce. Enjoy!