In a large skillet over medium heat, brown the ground beef or lamb. Once browned, drain any excess fat.
Add the diced onion and garlic to the skillet, cooking until the onion is translucent (approximately 3-4 minutes).
Stir in the diced carrots and cook for an additional 5 minutes until they start to soften.
Mix in the frozen peas, beef broth, tomato paste, Worcestershire sauce, thyme, rosemary, salt, and pepper. Bring this mixture to a simmer and let it cook for about 5-7 minutes, allowing the flavors to meld and the sauce to thicken slightly.
Transfer the meat mixture to a greased 9x13 inch casserole dish, spreading it evenly.
Spoon the mashed potatoes over the top of the meat mixture, smoothing it out with a spatula. If using, sprinkle the shredded cheddar cheese on top of the mashed potatoes.
Place the casserole in the preheated oven and bake for 25-30 minutes, or until the top is golden brown and the edges are bubbling.
Remove from the oven and let it cool for a few minutes. Garnish with fresh parsley before serving.
Notes
Feel free to add other vegetables or use different types of cheese.