Heat your oven to 200°C/Fan 180°C/Gas 6. Pull the stems from the centre of each mushroom and finely chop (keep the mushrooms whole).
Peel and grate the shallots, ginger and garlic. Pop into a bowl with the chopped mushrooms stems.
Halve the chilli and flick out most of the seeds and white bits (or leave the seeds in for a bit more heat if you like). Add to the bowl. Pick the leaves from the coriander. Set the leaves aside. Finely chop the stalks and add to the bowl.
Finely chop the cherry tomatoes and put them in the bowl. Finely grate the zest from the lime. Add that and squeeze in the juice from half the lime (keep the other half for later).
Tip the crab meat into the bowl. Mix together with a pinch of salt. Taste and add a little more salt if you think it needs it. This is your Thai crab stuffing.
Beat the egg and stir it through the crab stuffing. Lay the portobello mushrooms on a baking tray. Divide the mix and press into each mushroom, right to the edges. Drizzle 2 tsp oil over the mushrooms. Bake for 15 mins till the mushrooms are soft and the stuffing has browned.
While mushrooms are cooking, make your cucumber and coriander salad: use a veg peeler to peel long ribbons from the cucumber, turning it as you go. Finely chop the seeded middle. Pop both into a bowl.
Pour the rice wine vinegar into the bowl with 1 tsp oil. Scrunch everything together with a pinch of salt. Add most of the coriander leaves. Serve with the Thai stuffed crab mushrooms, garnished with the remaining coriander leaves and wedges of the remaining lime.