Mix 1/4 C light Mayo, 1 Tbl Dijon, 1 Tbl lemon juice, 1/4 C breadcrumbs and 1.5 Tbl Parm.
Spray olive oil in a 9X13 pan bottom.
Place Halibut filet's into the pan. Spread mayo / dijon mixture on the top of the filet's.
Melt the butter in a small bowl. (microwave) Mix in the balance of the bread crumbs and the parm, garlic and parsley into melted butter. Note - I used 4 Tbl of the butter, but upon double checking the recipe's I leveraged, they used substantially less. I bet you could easily get by on 2 tbl butter. Put the breadcrumb/herb/butter mixture on top of the fish - for an extra crispy topping.
Bake the fish at 350 degrees for about 12 - 14 minutes. Then put oven on Broil (change the racks in the oven if needed) for a couple of minutes (4) until the top is nicely brown.
(Note first time I made this - had about 1.25 lbs halibut and husband thought there was a smidge too much of the mayo / dijon mixture.).