Heat your oven to 200°C/Fan 180°C/Gas 6. Place a roasting tin on the top shelf to heat up.
Quarter the squash. Scoop out the seeds and discard them. Cut the squash into 2-3cm hunks. Peel the skin off if you like but it is edible, so leave it on for more texture. Pop the squash in a bowl.
Gloss the squash with 1 tbsp oil. Season well. Tumble into the preheated roasting tin. Cook for 30 mins or till the squash is tender and golden.
While the squash roasts, peel and thinly slice the onions. Warm a large pan over a medium heat for 1 min. Add a ½ tbsp oil, the onions and a pinch of salt. Let the onions sizzle for 8-10 mins till they get a little crisp. Spoon out of the pan and set aside.
Add the coconut milk to the pan with 400ml boiling water. Swirl in the Thai red curry paste. Bring to a gentle simmer.
Once the squash is roasty-toasty and tender, add it to the broth along with the crispy onions. Taste and adjust the seasoning. Ladle into bowls. Finely grate a little lime zest over each bowl. Serve with wedges of lime for squeezing.