Add butter, garlic, lemon zest and parsley in a bowl and mix together. Place mixture onto clingfilm and form into a log, twisting the ends to seal. Refrigerate until firm.
Prepare salad ingredients by combining avocado, red onion, alfalfa, and chilli in a bowl and tossing to combine. Set aside.
Meanwhile prepare the lobster by cutting them in half. Place lobster on its back on a tea towel to stop it slipping. Use a very sharp knife to cut the lobster in half lengthways. Wash the head cavity under water and dry with paper towel. Arrange lobster halves, cut-side up, in a lined baking tray.
Preheat barbecue to medium high. Take butter from the clingfilm and slice it into rounds. Place butter rounds over the lobster meat and cook until the butter starts to brown. Remove from heat.
Place lobster on plates and drizzle over any butter that has fallen into baking tray. Top with salad and serve immediately.
TOP TIP : Get ahead by making the butter log in advance and keeping it in the fridge until needed.