Heat some olive oil on a non-stick skillet over a medium-high heat. When hot, add the onions and garlic and cook until golden. Then add the mushrooms, season with salt and pepper, and cook until soft and starting to brown - around 10 minutes. When done, place onto a clean plate and let cool down for 5 minutes.
Preheat the oven to 200C (390F).
Meanwhile, in a large mixing bowl, combine the cooled mushroom mixture, egg, almond flour, and salt and ground black pepper to taste. Using your hands, mix until everything is evenly distributed.
Place the meat mixture into a baking dish and, using your hands, form a meatloaf. Bake for 40 minutes uncovered.
While baking, add the ketchup, Worcestershire sauce, and chipotle paste (if desired) into a small bowl and mix to combine.
After 40 minutes, remove the meatloaf from the oven and cover it with an even layer of the glazing mixture. Return to the oven and bake for an additional 10 mins or until fully cooked. The inner temperature should be 175F (79C).
Remove from the oven and let the meatloaf rest for 10-15 mins before slicing and serving.