For the Lime Chile Coriander Butter: Mix together the coriander, garlic, lime zest and juice, chile and butter until combined. Scrape into a small ramekin and refrigerate until ready to serve.
For the lobster: Preheat grill over medium-high heat and lightly oil the grates.
To kill the lobsters humanely, set each of them side by side on a board in front of you, claws facing towards the right. On top of the lobster shell, you'll see a cross shape just below the head. Stick the point of a sharp, heavy knife at the cross and push it through to the board. The lobster will be killed instantly. Afterwards, take the knife and slice down the middle of the lobster, lengthwise. Repeat with the second lobster.
Look at the insides of the lobsters. Remove and discard what you see in the sac behind the eyes, then you will see the little pale-colored claws. Pull those from the shells, and discard them as well. Remove, and reserve the green stuff, which, despite appearances, is a delicacy called the tomalley, the lobster liver. Cook's Note: You'll need to saute the tomalley gently if you want to eat it, as it will simply burn on the barbecue or griddle. Treat similarly any coral sac you may find, as this is the lobster roe.
Remove the claws as they cook since they coagulate at different rates compared to the rest of the lobster. Crack them open by hitting them with a sharp knife to help the heat penetrate the flesh. Place the lobster claws on the searing-hot grill, and cook for 6 minutes, then turn and add the lobster halves, cut-side down, to the grill. Cook the halves for 3 minutes, then turn them, and cook for another 2 minutes. The claws take another 6 minutes on their second side, so the pieces should be ready at the same time.
If you are using a griddle, get your griddle pan as hot as possible, and paint the lobsters with oil before setting them in the pan. The cooking times will be the same. The lobster will turn from bluish-black to bright orange when cooked. Serve the finished product with lemon or lime wedges.
For the prawns:
Mix together the oil, vinegar, garlic, parsley, and adjust the seasonings with salt, and black pepper. Pull the heads from the prawns and remove the little legs.
Cook's note: You can either discard these trimmings or use them to make fish stock.
With a sharp knife, make a shallow cut down the back of each prawn and, with your finger or a cocktail stick, discard the black vein. Add the tails to the oil and vinegar mixture, cover, and leave them to marinate in the refrigerator for about 1 hour. Meanwhile, if you intend to cook the prawns on wooden skewers, soak the skewers in cold water while the prawns marinate to prevent the skewers from burning on the grill.
Preheat the broiler or preheat a griddle on medium-high heat.
Remove the prawns from their marinade, and cook them either on the soaked wooden skewers on a very hot grill or under a hot broiler. Alternatively, grill them in a searing griddle pan. In either case, the prawns should cook for 3 minutes per side, and baste them with the marinade throughout the process. Serve the prawns or shrimp with lemon or lime wedges.