Preheat oven to 220°C. Place the potatoes in a medium saucepan. Cover with cold water. Bring to the boil over high heat. Cook for 5 mins or until just tender. Drain well.
Meanwhile, combine breadcrumbs, lemon rind, 2 tbs of the chives and half the dill in a shallow bowl. Place the flour and egg in separate bowls. Dip fish in flour and toss to coat. Shake off any excess. Dip in egg then place in the breadcrumb mixture and turn to coat. Lightly press to secure. Place on a plate.
Line 2 baking trays with baking paper. Place the fish on 1 tray. Spray with oil spray. Use a small knife to cut potato into quarters. Place on the remaining tray and drizzle with the olive oil.
Bake the potato and fish, turning once during cooking, for 20 mins or until the potato and fish are golden brown and cooked through.
Meanwhile, combine the yoghurt, cornichons, capers, remaining chives and remaining dill in a small bowl.
Serve the fish and chips with the yoghurt mixture, mixed salad leaves and lemon wedges, if desired.