1. Peel and finely chop the onion. Warm a medium-sized pan on a medium heat for 1 min, then add ½ tbsp olive oil and the onion. Season with a pinch of salt and pepper. Fry for 5 mins, stirring every so often, till the onion has softened.
2. While the onion fries, trim the ends off the courgette and aubergine and dice them both. Halve the red pepper, scoop out the seeds and white pith, and finely chop it.
3. Stir the chopped veg into the onion and season with a pinch more salt and pepper. Cook, stirring every so often, for 5 mins till the veg have started to soften and look glossy.
4. While the veg fry, peel and crush 2 of the garlic cloves. Drain the cannellini beans and rinse them under cold water.
5. Stir the garlic into the veg and cook and stir for 1 min. Tip in the cannellini beans and then add the tinned cherry tomatoes. Give everything a good stir to mix, then pop on a lid (or use a baking tray if you don't have a lid) and bring to the boil. Turn the heat down and simmer for 15 mins, stirring every so often, till the ratatouille has thickened and little and the veg are tender.
6. While the ratatouille simmers, make the pistou. Place a dry frying pan on a medium-low heat and tip in the breadcrumbs. Toast, stirring, for 2 mins till golden. Tip the toasted breadcrumbs into a mixing bowl.
7. Peel and crush or finely grate the remaining garlic cloves and add them to the breadcrumbs. Place the parsley, leaves and stalks, on a chopping board and then finely chop it. Chop as finely as you can. Add to the bowl and stir in 1 tbsp olive oil, 4 tbsp water and a pinch of salt and pepper. Taste and adjust the seasoning.
8. Taste the ratatouille and adjust the seasoning. Ladle the ratatouille into warm bowls and spoon the pistou over the top and serve.