First make the dressing: de-seed and finely chop the chilli. Mince or finely chop the garlic.
Mix together all the 'dressing' ingredients in a bowl. Add 2 tablespoons of water to this and stir again. Taste and adjust seasoning. Set aside.
Boil water in a small saucepan. Poach the prawns and squid for 3 mins over medium heat. Remove and rinse under cold water.
Remove the peel of the grapefruit (making sure to also remove the bitter white pith just beneath the peel). Slice into rounds, then remove any seeds. Chop into approx 2 inch pieces. Also chop the cucumber into 2 inch pieces.
In a large bowl, toss the cooked seafood, grapefruit, cucumber, mint and coriander leaves, and peanuts. Add the dressing and toss just before serving.