In a large bowl, combine the salmon, breadcrumbs, egg, mayo, mustard, lemon juice, onion, parsley, garlic powder, salt, and pepper.
Stir until just combined. If the mixture seems too soft or sticky, mix in a little more breadcrumbs until it holds together.
Shape into 5–6 even patties and place them on a plate. Chill them in the refrigerator for about 15–20 minutes so they firm up.
While the patties chill, make the sauce: In a small saucepan over medium heat, melt the butter.
Whisk in the flour to form a roux, and cook for 1 minute, stirring constantly.
Slowly add the milk, whisking continuously to avoid lumps. Cook for 3–5 minutes, or until the sauce thickens.
Season with garlic powder, salt, pepper, lemon juice, and dill. Stir well and keep warm on low heat.
Heat olive oil in a nonstick skillet over medium heat. Add the chilled salmon patties and cook for 3–4 minutes per side, or until they’re golden and heated through.
Transfer to a paper towel-lined plate to remove any excess oil.
Serve the patties hot, topped with a spoonful of lemon dill sauce. Add a garnish of extra dill or lemon wedges, if desired.