Preheat the oven to gas 7, 220°C, fan 200°C.
Pat the potatoes with kitchen paper and tip into a bowl.
Sprinkle over the flour, toss to coat, then transfer to a baking tray or shallow roasting tin (about 40 x 30cm).
Season, drizzle over 2 tbsp oil and roast for 10 mins until turning crisp and lightly golden.
Add the peppers, tomatoes and onion wedges to the tray and toss well in the leftover oil.
Roast for 15 mins until the veg is tender.
Put the baguettes on a baking sheet and cook to pack instructions underneath the traybake.
Whisk the lemon juice, sugar and 2 tbsp oil in a large bowl; season.
Toss in the lettuce and sliced onions, then mix to coat.
Stir the beans through the traybake, crumble over the cheese, then cook for another 5 mins until the cheese is just picking up some golden-brown tinges and everything is piping hot.
Scatter with the coriander to serve, alongside the salad and crusty bread.
