Preheat you oven to 325 degrees F.In a cast iron skillet or a dutch oven, sautee onions for a few minutes.In a separate bowl, toss the beef in a tbsp of flour (this will help thicken up the stew slightly as it cooks).Now add the beef to the skillet and fry until brown.Add in the vegetables along with the diced tomatoes and beef broth to the skillet (the beef should be ¾ submerged in the broth).Next, add the rosemary.Give the skillet a good stir and let come to a boil before putting it in the oven.Let the stew cook for 3-4 hours or until the beef is fork-tender.Garnish with a sprinkling of lemon zest and freshly chopped rosemary.