Preheat a barbecue or ridged griddle pan.
Chop the parsley, then zest & juice one lemon and chop the garlic. Put all in a mortar and grind it into a paste with the pestle, adding some olive oil gradually to it. Season with salt and pepper. The sauce should be textured and a bit oily. Set aside.
Finely chop the grilled chilli or red pepper.
Put the prawns in large bowl, drizzle with some olive oil and squeeze the other lemon over them.
Put them on the grill and cook for a couple of minutes on each side, until they turn pink (If the prawns were pre-cooked, i.e. pink already, just warm them through).
Transfer the cooked prawns into a large serving dish, add the chopped chilli or red pepper and pour over the dressing. Toss.
Serve warm or at room temperature.