Heat the oven to 200C/180C fan/gas 6. Heat the oil in a large frying pan over a medium-low heat and fry the onion until softened but not coloured, about 10-12 mins. Stir in the garlic and cook for 1 min more before tipping in the squash. Cook for 8-10 mins until the squash has started to soften, then stir in the tomatoes, mascarpone and spinach. Season well and cook for a few minutes more to warm everything through, then tip into a medium baking dish (ours was 22 x 22cm).

For the crumble, rub the flour and butter together or blitz in a food processor to a breadcrumb-like consistency. Stir in the cheese, walnuts and thyme, and season. Scatter the crumble over the squash filling, being careful not to pack it down. Bake for 30-40 mins until the squash is tender and the crumble is golden.