Peel and chop the onions. Wash and chop the tomatoes. Wash the meat, dab dry and rub Cajun spice on all sides. Tie into shape with kitchen string.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Heat the oil in a roasting pan and fry the meat thoroughly all around. Fry the onions. Add the tomatoes and fry briefly.
Season with salt and pepper. Deglaze with 1⁄2 l water, bring to the boil. Cover and braise in a hot oven for about 2 hours.
In the meantime, drain the jalapeños. Select the salad mix, wash and drain. Grate cheese roughly. Lift the roast from the stew. Season the stock with salt and pepper if necessary. Cut meat into slices and tear up.
Heat the tortilla flat bread according to the instructions on the packet and then cut into quarters.
Serve the meat, jalapeños, lettuce, cheese, crème fraîche and stewed stock together with the onions and tomatoes separately in small bowls. Cover the tortilla flat cakes as desired.