Cook the lentils:
1. In a medium saucepan, bring 2 1/2 cups water to a boil. Add the lentils, partially cover the pan with a lid, and cook until tender, about 30 minutes, stirring halfway through. Drain.
2. Pulse in a food processor until the texture is crumbly but not complete mush.

Make the loaf:
1. Preheat oven to 350ºF
2. In a large skillet, heat the oil over medium-high heat. Add the onion, celery, bell peppers and garlic and sauté until the onion begins to soften, about 3 minutes.
3. In a large bowl, combine  onion mixture, 1 cup crushed pistachios, lentils and seasonings: nutritional yeast, worcestershire, miso, umeboshi, thyme, truffle powder and tomato paste. Mix well.
4. The mixture should stick together, use parchment paper to form it into a 4x9 loaf

Assemble the Wellington:
1. Thaw puff pastry according to box direction
2. Pulse pistachios in a food processor until crushed but not powder
3. Roll out puff pastry between two sheets of parchment to 1/8-1/4 inch thick, keep it in a rectangle shape
4. Brush pastry with egg wash, top with a layer of 1 cup crushed pistachios covering the whole pastry, then add a 4 inch wide strip of the mushroom mixture in the middle
5. Place the loaf in the middle, lined up lengthwise with the mushrooms. Brush the loaf with dijon mustard
6. Roll up the loaf in the pastry, tuck in the ends and score the top to vent. Brush the whole Wellington with egg wash.
7. Bake for 20-25 minutes, until golden.
8. Let rest for 10 minutes, then slice to serve.
9. Serve with mushroom gravy or horseradish sauce