Heat 2 tablespoons of oil in a Dutch oven over medium-high heat. Add the chuck roast, season with salt and pepper, and sear on all sides, about 10 minutes. Remove the roast with a slotted spoon and set aside.
Heat another tablespoon of oil in the Dutch oven and add the onion, Anaheim pepper, and garlic. Saute the vegetables until they are softened, about 5 minutes. Add ¼ cup flour and stir to coat the vegetables. Add back the beef along with the remaining ingredients, except for the potatoes and carrots into the pot. Bring to a boil, cover the pot, and continue to braise the meat in the oven for 2 hours.
Remove the pot from the oven and add the potatoes and carrots. Continue to cook the stew in the oven for another 30 minutes or until the vegetables are tender. Season the stew with salt and pepper. Ladle the Spanish beef stew into bowls and top with sliced Spanish olives and chopped parsley. Serve immediately.
Notes
You can also prepare the stew in the instant pot. Follow steps 1-3, sauteing the beef and vegetables in the instant pot. After adding the beef along with the other ingredients back to the pot, set it to pressure cook on high for 45 minutes. Release the pressure and add the potatoes and carrots. Pressure cook for another 10 minutes and release the steam. Season and serve with garnishes.