Preheat oven to 240C (220C fan-forced) and line two baking trays with baking paper.
Scrub potato and sweet potato under cold water. Cut into 2cm-thick wedges. Pat dry with paper kitchen towel. Place in a large bowl. Add oil, rosemary and lemon rind. Toss well. Spread over one prepared tray. Place on top shelf in oven and bake for 15 minutes.
Meanwhile, cut fish into 2cm-3cm thick fingers. Sprinkle flour over a large plate. Place eggs in a shallow dish and combine breadcrumbs and parsley on a separate large plate. Dust fish fingers, one at a time, in flour, then dip in egg and coat in breadcrumbs, pressing on gently with fingertips.
Spray remaining paper-lined tray with oil. Arrange fish in a single layer on prepared tray. Spray fish with oil.
Remove wedges from oven. Turn and return to oven. Place the fish fingers on shelf under the wedges and bake both for 15 minutes or until fish is golden and cooked through and wedges are crisp and tender. Serve with salad leaves and lemon wedges.

Image credit: Ben Dearnley Photography