1.Using a mortar and pestle, crush fennel seeds with salt and pepper. Place sardines on a tray; sprinkle seed mixture on both sides. Cover with plastic wrap; refrigerate 20 minutes.
2.Meanwhile place ¼ cup olive oil, preserved lemon rind and juice in a screw-top jar; shake well. Season to taste.
3.Cook beans in a saucepan of boiling salted water for 2 minutes or until just tender; drain. When cool enough to handle, cut beans in half lengthways.
4.Using a mandoline or V-slicer, cut fennel into very thin slices. Using a vegetable peeler, peel cucumber into ribbons.
5.Place beans, fennel, cucumber and radish in a large bowl with dressing; toss gently to combine.
6.Heat remaining oil in a large frying pan over medium-high heat; cook sardines for 1 minute each side or until just cooked through.
7.Layer salad and avocado on plates, top with sardines; serve immediately.
Butterflied sardines are boneless with the two fillets attached. To do this yourself, cut off the head just behind the gills. With a small knife, cut along the belly, from head to tail then open out. Holding the spine at head end, pull it down firmly towards the tail end and snip with scissors to release it.