Pre-heat the oven to 180°C (fan)/200°C/gas mark 6.
Place one chopped onion and two cloves garlic in a large roasting tin.
Chop the aubergine, courgette, red pepper and peeled butternut squash into similar sized pieces - the smaller they are the quicker they'll cook - and place with the onion and garlic.
Pour over 2 tbsp olive oil and 1 tsp oregano and stir well to combine.
Place in the oven and roast for around 45 minutes stirring two or three times.
When the vegetables are soft pour over a 400g tin of chopped tomatoes and stir well.
Pour the amount of sauce you want blended into a blender, or use a handheld stick blender and blend. I usually leave half of the sauce unblended at this stage if I'm going to be eating it too as I prefer it this way.
Add water a little at a time if needed until you have a sauce-like consistency.
Store any un-used sauce in little pots or ice cube trays in the freezer.