Peel the onion, cut in half and then thinly slice. Rinse the peppers, trim, cut in half, remove the seeds and pith and cut into thin strips.
Rinse the celery, trim and cut into 1 cm (approximately 1/3 inch) thick slices. Peel the garlic and chop finely. Blanch the tomatoes, shock in ice water, peel, quarter, core and cut into thin strips. Trim the green beans, rinse and halve. Mix the vegetable broth with garlic, parsley, dill, thyme and olive oil and season with pepper. Layer the onion, pepper, celery, beans and tomatoes in a shallow baking dish. Pour the herb mixture over top and close the top tightly.
Bake in a preheated oven at 200°C for 1 hour.