Preheat the grill to a high setting.
Halve the lobster, chop meat from tail and claws, and returned it to shells.
Heat a griddle pan, oil the steaks, and cook for 3 minutes per side.
Rest the steaks in a warm place while finish cooking the other elements.
Mix butter with lemon zest and either dulse or watercress in a bowl.
Dot butter onto lobster tails and grill for 2 minutes until hot.
Heat vegetable oil to 180°C in a deep fryer or deep pan.
Fry the straw potatoes for 5 minutes until golden and drain on paper.
Combine the oil, vinegar, mustard, tarragon, and peppercorns to make the salad dressing.
Toss the lettuce with the dressing in a large bowl.
Serve steaks and lobster tails topped with remaining butter alongside fries and salad.