Preheat your oven to 400°F (200°C). Lightly grease a 9x13 baking dish and set it aside.
In a large skillet, heat the olive oil over medium heat. Add the lean ground beef and cook until it's nicely browned, then drain off any excess fat for a healthier base.
Stir in the diced onion and minced garlic, cooking for about 2 minutes until they become fragrant.
Add the diced carrots and potatoes, cooking for another 3 minutes while stirring. You'll notice some lovely caramelization starting, which adds natural sweetness and depth.
Mix in the tomato paste, Worcestershire sauce, dried thyme, salt, and pepper, ensuring everything is well combined.
Sprinkle the flour over the mixture and stir well to coat. Slowly pour in the beef broth, stirring continuously. Let it simmer gently for about 5 minutes until the sauce thickens nicely.
Finally, stir in the frozen peas and remove the skillet from the heat.
Transfer this flavorful filling into your prepared baking dish and set it aside.