Boil the cubed potatoes in salted water for 15-20 minutes until tender.

In a large skillet, heat oil over medium heat, add the diced onions and carrots, and sauté for 5 minutes until softened.

Add the ground beef or lamb to the skillet and cook until browned.

Stir in minced garlic and frozen peas, cooking for another minute.

Mix in the tomato paste, beef broth, and Worcestershire sauce, stirring until combined.

Allow the filling to simmer for 10 minutes.

Drain the potatoes and return to pot, mash with milk and butter until creamy.

Spread the meat filling in a baking dish and top with the mashed potatoes.

Bake in a preheated oven at 400°F for 25-30 minutes until golden on top.