Peel the sweet potato and cut it into 1/2-inch cubes for even cooking. Bring a pot of salted water to a boil and add the sweet potato cubes, simmering for 12-15 minutes until completely tender and easily pierced with a fork. Drain well and mash thoroughly until smooth with no lumps—this will create a creamy, spreadable topping layer for the lasagna.

Heat a large skillet over medium-high heat and add the ground beef, breaking it apart as it cooks for 5-7 minutes until browned and no pink remains. Add the diced red onion and minced garlic, cooking for 1 minute until fragrant. Stir in the curry powder, salt, and tomato paste, mixing well for 1 minute to bloom the curry and deepen the flavors. I find that blooming the spices in the meat releases their full aroma and creates a richer base than adding them later.

Add the taco sauce, drained canned tomatoes, soy sauce, and beef stock cube to the meat mixture, stirring to combine everything evenly. Add the frozen mixed vegetables and mix well, then reduce heat to medium-low and simmer for 10 minutes, allowing the flavors to meld and the sauce to thicken slightly. This simmering time lets all the ingredients get to know each other while the vegetables soften and the spices fully distribute throughout the filling.

Preheat your oven to 180°C (350°F). Spread half of the cooked beef curry mixture into the bottom of a baking dish, then arrange 3 lasagna sheets (breaking them to fit if needed) over the meat. Spread the remaining beef curry mixture over the sheets, then spread the mashed sweet potato evenly across the top as a creamy final layer. Sprinkle the grated cheese over the sweet potato, then bake for 30 minutes until the cheese is melted and the dish is heated through. The sweet potato on top acts like a savory mashed potato topping, which is the signature element that makes this shepherd's pie inspired.