How to Make It
Preheat oven to 400°F. Whisk together oil, garlic, lemon zest, lemon juice, and 1/2 teaspoon of the kosher salt and 1/4 teaspoon of the pepper in a large bowl. Add Brussels sprouts, leek, and red potatoes, and toss to coat. Spread the vegetables on a lightly greased, aluminum foil-lined rimmed baking sheet. Bake vegetables in preheated oven 10 minutes.
Meanwhile combine beef, sausage, carrot, onion, breadcrumbs, egg, and remaining 1/2 teaspoon each salt and pepper in a large bowl. Mix gently just until combined. Shape into 4 (2- x 3-inch) loaves. Remove pan from oven, push vegetables to 1 side, and carefully place meatloaves on pan. Return pan to oven, and bake until meat is cooked through and vegetables are tender, about 35 minutes.
Whisk together ketchup and soy sauce in a small bowl. Spread over meatloaves. Increase oven temperature to broil, and broil until sauce begins to brown, about 2 minutes. Divide meatloaves and vegetables evenly among 4 plates. Sprinkle with parsley.