Prepare the salmon mixture. In a large bowl, gently flake the leftover salmon with a fork, removing any skin or bones you might find. Be careful not to over-flake—some texture is desirable.
Add the binding ingredients. To the flaked salmon, add the beaten eggs, mayonnaise, and Dijon mustard. These ingredients help hold the patties together while adding moisture and flavor.
Incorporate the vegetables and seasonings. Add the diced bell pepper, onion, fresh herbs, garlic powder, salt, and pepper to the mixture. The vegetables add crunch, color, and nutrition.
Finish with breadcrumbs and lemon. Sprinkle in the panko breadcrumbs and lemon juice, then gently fold everything together until just combined. Avoid overmixing, which can make the patties dense.
Form the patties. Using your hands, shape the mixture into 8 equal-sized patties about 1/2-inch thick. If the mixture feels too wet, add a bit more breadcrumbs; if too dry, add a touch more mayonnaise.
Chill the patties. For best results, place the formed patties on a plate and refrigerate for 15-20 minutes to help them firm up. If you’re short on time, you can skip this step, but the patties may be slightly more delicate to handle.
Heat the cooking fat. In a large non-stick skillet, heat the olive oil or butter over medium heat until shimmering but not smoking.
Cook the patties. Carefully place the patties in the hot pan, leaving space between them. Cook for 3-4 minutes per side until golden brown and heated through. Work in batches if necessary to avoid crowding the pan.
Drain and serve. Transfer the cooked patties to a paper towel-lined plate to remove excess oil, then serve immediately with lemon wedges and your favorite sauce.