Preheat your oven to 220º C (430º F). Cube the butternut squash, coat it with olive oil and salt, spread on a baking tray, and roast for 25-30 minutes.

In a skillet, heat olive oil over low-medium heat. Add diced garlic; sauté for 2-3 minutes, then add chilli flakes for another minute.

Boil salted water in a large pot, cook spaghetti for 8-10 minutes until al dente, then drain, reserving some cooking water.

Mash half the roasted squash in the skillet with garlic and chilli, add the whole roasted pieces, and combine for 2 minutes.

Toss in the drained spaghetti and fresh spinach, adding reserved pasta water if needed for consistency.

Finish with lemon juice, season with salt and pepper, and serve topped with walnuts and lemon zest.