Prep the oven and pan: Preheat the oven to 350°F (180°C; 160°C fan). Lightly grease a standard loaf pan and set aside.
Sauté the aromatics: Heat the olive oil in a skillet over medium heat. Add the chopped onion and garlic and cook for 5-7 minutes, stirring occasionally, until softened and fragrant.
Mix the loaf: Add the cooked onion and garlic to a large mixing bowl with the lentils, walnuts, breadcrumbs, flax eggs, tomato paste, soy sauce, thyme, rosemary, salt, and pepper. Mix thoroughly until all the ingredients are evenly combined.
Shape the loaf: Transfer the mixture to the prepared loaf pan. Press it down firmly and evenly, then smooth the top with the back of a spoon or spatula.
Make the cranberry glaze: Add the cranberries, brown sugar, balsamic vinegar, Dijon mustard, cinnamon, orange zest, and water to a small saucepan. Bring to a gentle simmer over medium heat and cook, stirring occasionally, until the cranberries burst and the mixture thickens into a glossy glaze. Remove from the heat.
Bake the loaf: Place the loaf in the preheated oven and bake for 30-35 minutes, until firm and lightly crisp around the edges.
Glaze and decorate: During the final 15 minutes of baking, brush most of the cranberry glaze evenly over the top of the loaf. If using the carrot decorations, arrange them on top during the final 5 minutes of baking.
Cool and serve: Let the loaf cool in the pan for a few minutes before carefully removing and slicing with a sharp serrated knife. Serve warm with the remaining cranberry glaze and your favorite holiday sides.
Notes
Lentils: The 14 oz (400 g) canned lentils are measured before draining. Drain them thoroughly before adding them to the loaf mixture.
Breadcrumbs: Use dried breadcrumbs rather than fresh breadcrumbs. Their lower moisture content helps the loaf hold together and creates a firmer texture.
Loaf pan: A standard 9 x 5-inch loaf pan works best for this recipe. Press the mixture firmly into the pan so the finished loaf holds together well when sliced.
Cranberry glaze: The glaze will continue to thicken slightly as it cools. If it becomes too thick to brush onto the loaf, stir in a small splash of water.
Cooling: Let the loaf rest for a few minutes before removing it from the pan and slicing. This gives it time to firm up and makes cleaner slices.
Make ahead: The lentil loaf can be assembled ahead of time and refrigerated until ready to bake. For the best finish, prepare and add the cranberry glaze shortly before or during baking.