Chicken and Vegetable Stir Fry

Cut chicken breast into about 1.5-2 cm (approximately 1/2 to 3/4-inch) cubes and mix with curry paste. Peel onions and cut into thin rings. Rinse, trim and cut beans in half if necessary. Rinse, trim and cut zucchini lengthwise into quarters. Dice zucchini. Cut lemon into quarters lengthwise and slice. Rinse and halve pepper, remove seeds and ribs and cut into strips. Rinse and slice celery. Rinse marjoram, shake dry and strip leaves from stems. Cook beans in boiling salted water, about 3 minutes. Rinse with cold water and drain well. Heat oil in a large skillet or wok. Add chicken and cook over high heat, stirring. Transfer chicken to a plate, cover with aluminum foil and place in an oven at 100°C (approximately 200°F) to keep warm. Add vegetables to pan and stir-fry. Add broth and simmer, stirring, 5-8 minutes. Season vegetables with salt, pepper, soy sauce and oyster sauce to taste. Return chicken and juices to pan. Stir in marjoram and serve hot.