Heat an oven to 140C/120C Fan/Gas 1. Line a baking tray.
Place the tomatoes on the prepared tray and sprinkle the thyme leaves over the top, season with salt and pepper. Place in the oven and cook for 2 hours until dried out.
Lay out a sheet of cling film out that is about 30cm/12in square.
Halve the avocado, then use a mandolin to slice the avocado thinly, laying the slices side by side along the length of the cling film, leaving 5cm/2in on each end. Now squeeze lime juice over the avocado and season with sea salt and white pepper.
Take the white crab meat, checking that there is no shell or cartilage in the meat and then flake it into a bowl, lightly season adding the coriander and mayonnaise. Mix together and spoon out along the middle of the avocado. Tightly roll the avocado around the crab meat tying the cling film at each end and then put in the fridge for at least 1 hour.
Gently warm the grapefruit juice with the sugar syrup over a low heat and whisk in the xanthan gum until thickened.
Take the brown crab meat, smoked paprika and cream in a blender. Push the mixture through a sieve into a piping bag.
Just before serving, heat a frying pan until very hot, fry the scallops in a little olive oil, for about 1 minute on each side.
Take the cannelloni out of the cling film and place in the centre of the plate, leave whole. Then pipe the brown crab meat in little patches all around, alternating with the pink grapefruit gel. Then place the scallops and sea herbs neatly around the plate. Garnish with the tomatoes and coriander cress and serve.