Dice up the onion.

Put a few large dollops of margarine in a skillet, and saute the onion.

After a few minutes (don't let the onions go translucent, they don't need to be THAT sauteed) add the salmon and let it fry for a minute or two too.

Stir in the breadcrumbs.

Let it all fry for a little while, stirring frequently, until the breadcrumbs have just browned a little. You can form it into a patty if you like though it'll just barely stick together with these quantities.