Sauté the onions and garlic in a large skillet over medium heat until the onions turn translucent.

Add the diced carrots and ground beef to the skillet. Cook until the beef is browned, about 5-7 minutes.

Season the mixture with Worcestershire sauce, thyme or rosemary, salt, and pepper. Stir for another 2 minutes.

Mix in the frozen peas and simmer for an additional 5 minutes.

Boil the potatoes in a large pot until fork-tender, about 15-20 minutes. Drain and mash with butter and milk.

Preheat your oven to 400°F (200°C). Spread the meat mixture in a baking dish and top with mashed potatoes.

Bake for 25-30 minutes or until the top is golden brown.