Heat the oil in a large skillet over medium heat. Lightly brown the meat in batches, then transfer the browned beef to a plate and set aside.
Dump the tomatoes, including the juice, into the slow cooker. Add the onions, celery, carrots and potatoes. Sprinkle Italian seasoning over the vegetables and then add the beef and any accumulated drippings. Add the bay leaves. Pour 2½ cups of the beef broth over the top and give the mixture a stir. Cover and cook on low for 8-10 hours.
20 minutes before serving, add the peas (no need to defrost), salt and pepper to the stew.
In a small bowl, whisk together the flour and remaining ½ cup of beef broth, making a smooth paste. Stir into the stew and cook until thickened, about 15-20 minutes. Remove bay leaves before serving.