Wash the pumpkin, cut in half and remove the seeds. Cut into cubes and spread on a baking sheet lined with baking paper. Sprinkle with oil, pepper, salt and chili flakes. Roast in the oven for about 20 minutes until completely cooked and tender. Mash or puree the squash until smooth (keep a generous handful of cubes aside) and mix with the broth.
In a large skillet, heat a little oil and gently sauté the chopped onion. After about 3 minutes, add the garlic and thyme and fry gently for a few more minutes.
Add the rice to the pan and fry gently for about 5 minutes, until all the rice grains are shiny.
Now add the pumpkin puree broth in parts. Add enough to just cover the rice and stir well. Then let it simmer until the rice has absorbed all the liquid before adding more stock. Continue this way until the rice is al dente.
Clean the mushrooms and cut into strips. Heat a little oil in a frying pan and fry the mushrooms over medium-high heat until golden brown.
Cut the sage leaves into thin strips. Mix the mushrooms and sage into the risotto, along with the noble yeast. Season to taste with salt and pepper. Garnish with the cubes of roasted squash.