Preheat: Preheat your oven to 350.
Make your flax egg: In a small bowl, add your ground flaxseed and 2.5 tablespoon water. Mix to combine and set to the side. This will thicken as it sits and will later be our "egg" substitute.
Sauté your veggies: Bring a medium nonstick pan to med-high heat on the stovetop. Add just a bit of water to prevent sticking, and add your onion. Allow to sauté for 2 minutes, stirring occasionally and adding small amounts of water as needed to prevent sticking. Add the garlic, carrots, and mushrooms to the pan. Cook for 4 minutes. Continue to stir occasionally and add small amounts of water as needed to prevent sticking. Turn the heat down to medium. Add the vegan Worcestershire sauce and tomato paste. Stir to coat all the veggies evenly, and allow to cook 1-2 more minutes. Turn off the heat and set the pan aside to cool. Mash your lentils: Using a potato masher (or another utensil of choice), mash your cooked lentils. You want these to still have some texture to them, so they don't have to be perfectly smooth.
Make your loaf mixture: In a separate bowl, combine the breadcrumbs, flour, thyme, oregano, onion powder, garlic powder, nutritional yeast, and salt. Mix so that everything is evenly incorporated. To your breadcrumb mixture, add your sautéd veggies, mashed lentils, flax "egg", and water chestnuts. Mix to combine everything. Wrap your loaf in puff pastry: Lay out your puff pastry on a cutting board. If your puff pastry is rectangular, position it so that it is taller than it is wide. Using your hands (this might get a little messy!), form your lentil mixture into one large log-shaped loaf. Place your loaf, taller than it is wide, in the center of your puff pastry, making sure there's about an inch of puff pastry above and below the loaf. Using a knife (or a pizza cutter), cut 7-10 straight horizontal lines on both the right and left sides of the pastry. The cuts should start at the outside edge of the puff pastry and end at the outside edge of the veggie loaf. This will create multiple strips on either side of the loaf so that it kind of looks like spider legs coming out of the loaf. Take the top edge of the puff pastry and fold it up onto the end of the loaf, then wrap the ends of this piece around the upper perimeter. Repeat this step on the bottom.Now, starting at the top, take the next strip from the top right and fold it over the loaf towards the left. Take the left strip and fold it over towards the right, so that it slightly covers the end of the previous strip. Continue this all the way down, alternating between the right and left, until you have run out of pastry. Depending on the size of your strips, your design may look slightly different than my version (as long as it's covered in puff pastry, it'll be delicious!). Transfer your Wellington to a prepared baking sheet (with either a silicone baking mat or parchment paper) Brush on your almond milk wash: Combine your almond milk and maple syrup in a small bowl. Using a pastry brush, brush this onto your puff pastry. You want as much of the pastry to be coated as possible!
Bake your Wellington: Place your baking sheet into the preheated oven and allow your Wellington to bake for 45 minutes. (If the puff pastry isn't quite golden brown after 45 minutes, you can allow it to bake for 5 minutes more).
Enjoy: Remove from the oven, allow to cool a few minutes, and enjoy! Best served with a few spoonfuls of Joyful Balance Vegan Mushroom Gravy on top!