For the tian, preheat the oven to 200C/180C Fan/Gas 6.
Heat the oil in a large ovenproof sauté or frying pan over a medium–high heat. Add the peppers, season with salt and pepper and sauté for 1–2 minutes.
Transfer to the oven and roast, uncovered, for 10 minutes until soft. Transfer the peppers to a large bowl and cover with cling film. Leave them to sweat for 10 minutes.
Transfer the peppers to a sieve or colander and rinse off the skins under cold running water. Cut the peppers into quarters, remove the membranes and seeds and place on kitchen paper to dry.
For the mayonnaise, put the egg yolks in a bowl with the white wine vinegar, Dijon mustard and a pinch of salt and whisk until combined. Slowly drizzle in the oil, whisking continuously to emulsify the mixture and making sure each drop of oil is fully incorporated before adding more. Once all of the oil has been added, the mayonnaise should be thick and glossy. Season with lemon juice and salt to taste. Cover and chill until required.
Drizzle the avocado with 1 teaspoon of the lemon juice. Place the crab in a bowl and add just enough mayonnaise to bind it together. Any remaining mayonnaise can be used in another recipe. Add the chives, coriander, curry powder and the remaining lemon juice. Season with salt and pepper.
Line a 20-cm/8-in square cake tin with three layers of cling film. Arrange a layer of the peppers over the base, peeled side down, so the base is covered. Season with salt and pepper. Add half of the crab mixture and spread it out evenly to cover the peppers. Add a layer of avocado slices and then another layer of crab. Finish with a layer of red pepper. Cover with cling film and leave in the fridge for at least 1½ hours.
Turn the tian out on to a chopping board and remove the cling film. Sprinkle over the sea salad, cut into squares and serve immediately.