Preheat oven to 180°C. In a flameproof casserole dish with a tight-fitting lid, heat oil over medium-high heat. Dredge the chicken in flour. Sauté until golden, about 4 minutes per side. Transfer to a plate.
Add fennel to pan. Reduce heat to medium. Cook, stirring frequently, until fennel is golden, 7 minutes. Add garlic; cook 1 minute. Add stock, lemon juice, salt, rosemary, thyme and pepper. Bring to the boil. Add chicken, cover, place in oven.
Cook until chicken is done, about 35 minutes. Stir in the white beans and green beans. Bake a further 5 minutes.