Cut the meat into pieces of about 1½ cm. Heat 2 tablespoons of olive oil in the casserole dish and fry the meat on a high heat for 5 minutes until golden brown. Sprinkle with salt and pepper to taste and remove the meat from the pan with a slotted spoon.
Heat the rest of the olive oil in the pan, add the onions and celery and stir-fry for 5 minutes until the celery is soft. Cut 1 pepper into 2cm pieces and add to the pan. Put the meat back into the pan together with the oregano and 500 ml of water. Bring to the boil, put the lid on the pan and simmer the meat for about 2 hours until completely cooked (longer if necessary). Use the smallest burner of the stove and if necessary, insert a flame distributor. Stir occasionally. Add some extra hot water if necessary.
Cut the remaining peppers and the spring onions into rings. When the meat is cooked through, add the peppers and cook for 5 minutes. Then add the rinsed beans. Add the spinach leaves just before serving. Season the stew with salt and freshly ground black pepper. Garnish with spring onions.