Preheat oven to 400 F.
Line the bottom of a baking dish with aluminum foil (optional but highly recommended for easy cleanup). Use any size oven-safe dish that will fit the salmon - 8x8, 9x9, 9x13, cookie sheet, etc.
Carefully check your salmon pieces for small bones. If you find any, use pliers to pull them out before cooking. (also optional, but it makes dinner much more enjoyable if the bones are already removed). WASH YOUR PLIERS.
Rinse salmon filet and place skin-side down in the prepared baking dish.
Sprinkle salt, pepper, onion powder, and dill evenly over the fish. (see note)
Cut the butter into small pieces, and place them evenly down the center of the filet. (If there is a higher/taller part of the fish, put the butter along that line - it will melt and you want it to get on as much of the salmon as possible when it does)
Bake in a preheated oven for 25-30 minutes; longer for bigger salmon. Salmon is done when it is at least 145 degrees F in the fattest part.
Use a spatula to lift the fish right off the skin and onto a serving platter. The skin should stay stuck to the aluminum foil and the salmon should separate easily.