Preheat oven broiler to high.

In a large oven-safe skillet over medium-high heat, brown the ground lamb and diced onion until meat is cooked through, approximately 7-9 minutes.

Drain excess fat from the skillet.

Stir in tomato paste, frozen peas and carrots, beef broth, Worcestershire sauce, and dried thyme.

Simmer for 5 minutes until the sauce has thickened slightly; season with salt and pepper.

Spread the prepared mashed potatoes evenly over the meat mixture.

Sprinkle with shredded cheddar cheese.

Place the skillet under the broiler for 3-5 minutes or until the potatoes are lightly browned and cheese is melted.

Let rest for 5 minutes before serving.