Preheat the oven to 400°F (200°C).

In a large skillet over medium heat, cook the ground beef or lamb until browned. Drain excess fat.

Add the diced onion and minced garlic to the skillet and sauté until the onion is translucent, about 5 minutes.

Stir in the frozen mixed vegetables, tomato paste, Worcestershire sauce, thyme, rosemary, salt, and pepper. Cook for an additional 5 minutes, then remove from heat.

While the meat mixture is cooking, place the cubed potatoes in a large pot and cover with water. Bring to a boil and cook until tender, about 15-20 minutes.

Drain the potatoes and return them to the pot. Add the milk, butter, minced garlic, salt, and pepper. Mash until smooth and creamy.

In a 9x13 inch baking dish, spread the meat mixture evenly. Top with the garlic mashed potatoes, spreading them out to cover the meat completely.

Sprinkle the shredded cheddar cheese on top of the mashed potatoes.

Bake in the preheated oven for 25-30 minutes, or until the cheese is bubbly and golden brown.

Let cool for a few minutes before serving.