Pecan Parmesan Halibut

2 lbs. Halibut fillets
1/2 c. Mayonnaise
Parmesan
1/2 onion diced
1/2 c. Chopped pecans
6 Tbls. Butter
1tube ritz crackers

Preheat oven to 350°. Line a 9 x 13 pan with aluminum foil, and spray with Pam.Generously salt and pepper the fillets.  Apply the mayonnaise to the top of the fish, and generously sprinkle Parmesan over the top of that.  Sprinkle chopped onion and pecans next. In a bowl mix together the Ritz and butter and layer over the top. Bake for 30 minutes.