1.Shell and devein prawns, leaving tails intact. Remove heads and beaks from octopus. Cut fish into 2.5cm pieces. Combine seafood in large bowl.
2.Using mortar and pestle, crush seeds and peppercorns coarsely, add to seafood with vinegar, garlic and oil, toss gently to combine. Cover, refrigerate 3 hours or overnight.
3.Make mustard dressing. Place ingredients in screw-top jar, shake well.
4.Thread seafood, alternating varieties, on skewers, cook on heated lightly oiled grill plate (or grill or barbecue) until seafood is just changed in colour and cooked as desired.
5.Meanwhile, discard dark outer leaves of radicchio, tear inner leaves roughly. Combine radicchio in medium bowl with fennel, parsley and dressing, toss gently to combine.
6.Serve seafood skewers on salad.
Use green peppercorns in brine if you can’t find the dried variety, rinse then drain them thoroughly before using. You need to soak eight bamboo skewers in water for at least an hour before use to prevent splintering and scorching. Any firm white fish fillet, such as ling or blue-eye, can be used in this recipe.