Put the curry, cumin, fennel, peppercorns, cayenne, and salt in a spice mill or clean coffee grinder. Grind to a fine powder and set aside.
Rinse the calamari tubes under cool water and pat dry. Split the bodies from top to bottom so you have 2 triangular pieces from each. Put the calamari, lobster, and prawns on a platter and drizzle with a nice dose of olive oil so the seafood is well coated; season with a fair amount of salt and pepper.
Place a large grill pan on 2 burners over medium-high heat or preheat a gas or charcoal grill and get it very hot. Take a few paper towels and fold them several times to make a thick square. Blot a small amount of oil on the paper towel then carefully and quickly wipe the ridges of the grill pan or the hot grates of the grill. Place the lobster on the grill, shell-side up, and cook for 5 minutes until the shell begins to turn reddish-orange. Turn the lobster tails over and lay the calamari, prawns, green onions, and limes (cut side-down) on the grill too until everything is slightly charred. Grill the calamari for 2 minutes per side, and no longer, otherwise they will get rubbery.
Put the grilled mixed seafood and green onions on a large platter and sprinkle a little of the spice mix all over. Squeeze the grilled limes over the shellfish and serve immediately.