Slice the mushrooms. Halve the pepper and scoop out the seeds and white bits. Chop the pepper into small pieces. Peel and thinly slice the garlic.
Heat 1 tbsp oil in a large frying pan over a medium heat. Tip the diced chicken into the pan and fry for 5 mins till golden. Add the mushroom and pepper. Cook for 3 mins. Add the garlic and cook for 1 min.
Pour in the chopped tomatoes. Half fill the tin with cold water and add that too. Stir together. Cover and simmer for 20 mins.
When the sauce has cooked for 10 mins, put the spaghetti in a large pan. Cover with boiling water. Add a pinch of salt. Bring to the boil and cook for 6-8 mins till al dente (soft with a slight bite).
Finely shred the sage leaves and set aside.
Drain the pasta and tip back into the pan. Drizzle over ½ tbsp oil and season with salt and pepper.
Taste your sauce. Add seasoning if you think it needs it. Stir through most of the sage leaves. Serve the sauce on top of the spaghetti in warm bowls. Sprinkle over the remaining shredded sage.
Tip: An extra tipple^
For a richer sauce, pour in a glass of red wine instead
of adding the water with the chopped tomatoes.