Add the tomato paste, beef broth, Worcestershire, rosemary, thyme, and stir to combine. Bring to a boil, reduce the heat to low, cover and simmer slowly 10 to 12 minutes or until the sauce is thickened slightly.
Add the corn and peas to the lamb mixture and spread evenly into an 11 by 7-inch glass baking dish. Top with the mashed potatoes, starting around the edges to create a seal to prevent the mixture from bubbling up and smooth with a rubber spatula.