Preheat oven to 350 degrees F.

Line a baking dish with foil, grease lightly, place salmon skin side down on foil. Sprinkle with lemon pepper seasoning and onion salt. Top with onion and lemon slices, dot with butter and fold foil around salmon (like a pouch) and seal tightly.

Bake salmon for 30 minutes.

Meanwhile, Combine all the sauce ingredients in a bowl, mix until smooth and serve with salmon.