Wash leg of lamb, dab dry and rub with oil, salt and pepper. Peel and quarter the onions. Cut garlic into slices. Put everything into a roasting pan and braise in the preheated oven (electric cooker: 175 °C/ gas: level 2) for about 2 1/2 hours.
Deglaze gradually with 1/4 litre of water and the wine. Cut the tomatoes crosswise, briefly blanch with boiling water. Skin and halve the tomatoes. Drain the beans. Add both with the herbs to the meat 30 minutes before the end of the cooking time.
Season with salt and pepper.