Preheat the oven to 375F. Spray a 9x5 loaf pan. Line the bottom with parchment paper, allowing extra to hang over each side.
Fill a large soup pot with water and add the lentils. Place over medium heat and cover. Bring to a boil. Reduce the heat to a simmer and cook for about 30 minutes. Strain through a colander when lentils are cooked all the way through.
Meanwhile, heat olive oil over medium heat in a large skillet. Add onions and sauté, stirring frequently, for 5 minutes until onions are translucent and fragrant. Add garlic, carrots, celery, and mushrooms and sauté for another 5 minutes until vegetables are tender and lightly browned. Remove from heat. In a food processor combine sautéed vegetables, lentils, and the remaining ingredients for the vegan meatloaf. Pulse until well combined. Some texture should remain. Once about half your ingredients are well blended, transfer them to a bowl and mash the rest together with a potato masher or your hands.
Transfer the meatloaf to the prepared loaf pan, cover in tin foil, and bake for 30 minutes.
Meanwhile, mix together the ingredients for the tomato maple glaze in a small bowl. When the loaf is ready, pull it out, remove tin foil, and evenly cover the top with the glaze. Return to oven, uncovered, and bake an additional 10-15 minutes.
When the tomato glaze starts to brown at the edges and the lentil loaf is firm, remove from oven and let cool 15 minutes before slicing. This allows the meatloaf to firm up as it cools.
Serve with Cauliflower Mashed Potatoes and Maple Balsamic Brussels Sprouts for a hearty holiday meal.