'Full of veg' tomato sauce

INGREDIENTS

• olive oil
• 2 small onions, peeled and chopped
• 1 small leek, chopped and washed
• 2 sticks celery, trimmed and chopped
• 2 red peppers, chopped
• 2 courgettes, grated
• 2 carrots, grated
• 1 large pinch dried oregano
• 2 bay leaves
• 4 x 400 g tinned plum tomatoes
• 1 small butternut squash, peeled and seeds removed, grated
• sea salt
• freshly ground black pepper