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.
When the vegetables are soft pour over a 400g tin of chopped tomatoes and stir well.
Add water a little at a time if needed until you have a sauce-like consistency.