Preheat oven to 375°F (190°C).
In a large skillet, brown the ground beef over medium heat until fully cooked. Drain excess fat.
Add chopped onion, carrots, and garlic to the skillet. Cook until vegetables are softened.
Stir in tomato paste, Worcestershire sauce, and beef broth. Simmer for 10 minutes or until the mixture thickens slightly.
Add frozen peas and cook for an additional 2 minutes. Season with salt and pepper to taste.Transfer the beef mixture to a baking dish. Spread mashed potatoes evenly over the top.
Optional: Sprinkle shredded cheddar cheese on top of mashed potatoes.
Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and the filling is bubbly.
Let it cool for a few minutes before serving.