Prep the fish. If using fresh or frozen fish, poach, steam, or bake until just cooked and flaky. Let it cool, then flake into large pieces. If using canned, drain well.

Make the base. In a large bowl, combine mashed potatoes, egg, onion, herbs, lemon zest, lemon juice, Dijon, garlic powder, paprika, 3/4 teaspoon salt, and 1/4 teaspoon pepper.

Fold in the fish. Gently mix the flaked fish into the potato mixture. Keep some pieces chunky for better texture. Taste and adjust seasoning.

Shape the cakes. Divide into 8 patties (about 1/3 cup each). Chill on a tray for 15–20 minutes to firm up. This helps them hold their shape.

Coat with crumbs. Spread breadcrumbs on a plate. Press each patty lightly into the crumbs on both sides. Shake off excess.

Prepare the pan. Heat oven to 425°F (220°C). Line a baking sheet with parchment and brush or spray with oil. Arrange the cakes and brush the tops with oil.

Bake until golden. Bake 12–15 minutes, flip, brush with a little more oil, and bake another 8–10 minutes until crisp and lightly browned.

Serve hot. Squeeze with lemon and serve with a quick yogurt or tartar sauce and a simple salad.