Heat your oven to 180°C/Fan 160°C/Gas 4. Slice a little off the bottoms of the squash so they sit up straight. Slice the top off each squash to make lids. Scoop out the seeds. Place the squash on a baking tray, lids on. Roast for 30 mins till the flesh is soft.
Tip the rice into a bowl. Cover with cold water and whisk for a few mins till the water is cloudy (this is the starch). Drain and rinse the rice. Tip into a pan. Cover with boiling water.
Add a pinch of salt to the rice pan. Bring to the boil. Simmer for 5 mins till the rice is nearly cooked, then drain well.
While the rice cooks, finely slice the mushrooms. Finely chop the lime leaves (see our tip) and chillies, flicking out the seeds for less heat. Peel and grate the garlic and ginger.
Tip the mushrooms into a deep frying pan or wok with a splash of water. Cook over a medium heat for 5 mins, stirring often till the mushrooms are juicy. Add the lime leaves, chillies, garlic and ginger. Season well. Cook and stir for 1 min till the pan smells aromatic.
Stir the rice into mushrooms. Season. Take the squash out of the oven and drain off any excess water.
Spoon the mushroom stuffing into the squash shells. Return them to the oven, lids on, and roast for another 10 mins. Serve immediately with the lamb’s lettuce on the side.