Preheat the oven to 200°C / 400°F / Gas mark 6.
Season the chicken inside and out with salt and pepper, then stuff the cavity with 1 of the lemons and the thyme.
Sit in a large roasting tin and drizzle with olive oil and roast for 40 minutes.
Remove the tin from the oven, then scatter the ciabatta pieces around the chicken and tear over the prosciutto.
Add the garlic and remaining lemon halves to the tin.
Roast everything together for 40 minutes further until the croutons and prosciutto become crisp.
Remove from the oven, transfer the chicken to a plate and leave to cool.
Remove the croutons and prosciutto, and set aside.
Cook the green beans in a pan of boiling water for 5 minutes.
Drain, cool under cold water then tip into a large bowl with the spring onions and parsley.
Squash the roasted lemon and garlic in the roasting tin with a potato masher.
Remove all the skin from the garlic, then stir in the olive oil and lemon juice with a little salt and pepper then scrape the bottom of the tin to get all the sticky chicken juices into the dressing.
Stir in any resting juices from the chicken and set aside.
When the chicken is cool enough to handle, strip the meat away from the bones.
Before serving, add the dressing, chicken, croutons, prosciutto, salad leaves, rocket, cherry tomatoes and cucumber slices to the green bean mix in the bowl, toss together and scatter over a large serving platter.