In an oven-proof skillet over high heat, add the ground beef and cook, crumbling as it cooks, until browned, around 5 minutes. Add garlic, onion, and carrots, and continue to cook for an additional 2 minutes, or until the carrots and onion are just softened. Add the tomato paste and cook for 30 seconds.
Combine the cornstarch with 1/4 cup of the beef stock and add to the beef mixture. Add the remaining beef stock, Worcestershire sauce, salt, pepper, and peas. Stir gently to combine and cook for 2 minutes.
Spoon the mashed potatoes over the beef mixture, then place under the broiler for 5 minutes, or until lightly browned. Garnish with paprika, salt and pepper, and serve immediately.