Preheat the oven to 200°C, fan 180°C, gas 6. Heat half the olive oil in a large ovenproof casserole dish, add the aubergine and fry over a medium-high heat for 5 minutes until lightly charred. Remove from the pan and set to one side.
Add the remaining oil to the pan, add the onions and peppers and fry for 5 minutes until softened and lightly charred. Reduce the heat and add the garlic and courgettes. Cook for 2-3 minutes before adding the wine, tomatoes, tomato paste and 150ml water.
Add the aubergines, bring to the boil, reduce the heat and then simmer for 15 minutes. Stir in the cannellini beans and parsley and season to taste.
Cut the baguette into slices and cut each slice in half again to make around 20 thin slices. Place them on top of the casserole, garlic butter side up, and bake in the oven for 20 minutes until golden.