Place skinnless chicken breasts, crushed garlic,small potatoes and springs thyme in the base of a flameproof casserole dish. Pour over stock to cover chicken completely. Bring to the boil, then cover pan and simmer very gently for 10 minutes.
Add pieces of butternut pumpkin, then cover and simmer for 10 minutes more, or until the pumpkin is tender.
Lift out chicken and vegetables, set aside on a serving platter and keep warm, covered with foil. Boil stock until reduced by half, then add greens and olives and simmer for 3 to 4 minutes, or until cooked but still bright green. Season broth with salt and pepper and pour over chicken to serve.
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