Chop all vegetables and your sausage. I tend to slice then quarter the sausage. If necessary use latex gloves when chopping chillies.
Take a large pan, heat to medium add 1 to 2 tablespoons of oil. Once oil is getting warm add the garlic, dried spices and oregano. Once starting to cook add mushrooms, green pepper and chillies cook for around 10 minutes until starting to colour and soften.
Add sausage and onion and cook for a further 5 to 10 minutes. Remove from heat, season with salt and pepper and add passata and stir. Add chopped tomatoes, stir and add 3 tablespoons of tomato puree.
Return to heat add stock, stir through, taste, add more puree if you wish. Simmer for about 15 minutes, then it's ready! If the sauce if too runny you can use cornflour to thicken a bit, add when just warm not hot and stir through.