Make the shellfish oil1. Preheat the oven to 400F (200C). Place the lobster heads in a roasting pan and roast for 40 minutes or until they are bright red. Break up the heads into small pieces and place in a small saucepan with the tomato paste and grapeseed oil. Heat the mixture over medium-low heat for 10 minutes, then cool and refrigerate for 2 days.2. Strain the oil through a fine-mesh sieve lined with cheesecloth and discard the solids. Refrigerate until ready to use or for up to 2 weeks.Make the vegetables3. Preheat the oven to 350F (175C). Place the beets, onions, thyme, and olive oil in an ovenproof pan. Cover the vegetables and roast for 30 minutes. Add the scallions and replace the cover. Continue to roast for 20 more minutes, or until the vegetables are tender. Peel the onions and beets and cut the beets in half. Season to taste with salt and pepper.Make the sauce4. In a blender, pure the scallions, chiles, garlic, ginger, coriander, black pepper, lime leaves, lemongrass, basil, cilantro, olive oil, and lime zest and juice; pass through a fine-mesh sieve. Add the coconut milk and season to taste with salt and pepper. Warm just prior to use.Make the langoustines5. Heat a saute pan over medium heat. Add the shallots and shellfish oil and cook for 2 minutes. Add the langoustines. Increase the heat to high and continue to cook the langoustines for 2 to 3 minutes on each side, or until just cooked through. Remove the langoustines from the pan and season to taste with salt and pepper.6. Add the lettuce to the same pan and quickly wilt it in the hot pan; transfer to a bowl and season to taste with salt and pepper. Slice each langoustine into 4 pieces.Assemble the dish7. Cover the center of each plate with a generous amount of the green curry sauce. Arrange some of the wilted lettuce, langoustines, and vegetables on top of the sauce. Drizzle the shellfish oil around the plate and top with the sliced basil and pepper.