Combine all slaw ingredients in a large mixing bowl. Cover with plastic wrap and refrigerate until ready to serve.
Make the avocado mayonnaise:
Mash the avocados in a small mixing bowl. Add the remaining ingredients and stir to combine. Cover with plastic wrap and refrigerate until ready to serve.
Make the burgers:
Put the salmon and liquid from the can in a large mixing bowl and flake the salmon with a fork. Add the breadcrumbs, eggs, chili powder, chilies, corn, and scallions. Mix well. Form into 8 tightly-packed patties, about ½-inch thick.
Heat the oil in a large skillet over medium-high heat. Fry the patties in batches (do not over-crowd the pan), cooking for 3-4 minutes per side or until nicely browned.
To serve:
Spread the bottom bun with avocado mayonnaise. Top with a salmon patty. Top the patty with some slaw and the top burger bun.