1Line two baking sheets with parchment paper, spray with non-stick spray, and set aside. Have a small bowl of water and a clean, floured pastry board or flat surface ready.
2Using a food processor fitted with the S blade, process the walnuts into very small bits. Scrape the walnuts into a large mixing bowl and set aside.
3Add the brown rice and chickpeas to the bowl of the food processor and process until the mixture forms a coarse mash. Add this mash to the mixing bowl along with the oat bran, sage, marjoram, thyme, onion powder, soy sauce, mustard, and peanut butter. Using your hands, knead the mixture well until it is thoroughly mixed and holds its shape. Cool completely (if the filling is too warm it will melt the puff pastry and the pastry won’t bake up puffy and crisp).
4Unfold the first sheet of puff pastry on a floured pastry board or flat surface (it should still be cold, but thawed enough to unfold without cracking). Using a rolling pin, roll the pastry out into a 12 × 12-inch square. Cut the sheet into six rectangles, each about 6 × 4 inches.
5Scoop up a handful of the nut loaf mixture and form it into a small rectangular loaf, about 3 × 1 × 3/4 inches. Place the loaf in the center of a piece of puff pastry. Dip your fingers in the bowl of water and lightly wet the top of the loaf.
6Fold the short ends of the puff pastry up over the loaf, then fold the long edges up, using a bit of water on the edges of the pastry to help seal it shut. The loaf should be completely encased in puff pastry.
7Place the Mini Wellingtons, seam side down, on the prepared baking sheets. Repeat with the other sheet of puff pastry and the remaining bean and nut mixture. Lightly brush the pastries with olive oil.
8You may score the tops of the puff pastry with a decorative design using a very sharp knife or razor blade. Don’t cut completely through the puff pastry.
9Cover the baking sheets completely with plastic wrap and refrigerate overnight or until ready to bake.
10When ready to bake, preheat the oven to 400°F (give the oven plenty of time to warm up to ensure a good puff pastry crust). Bake for 25 minutes, until the crust is puffed and golden and the inside is heated through.
VARIATION: We adults love this version with mushrooms: Sauté 2 cups minced button mushrooms, 1 minced garlic clove, and a pinch of salt in 2 teaspoons olive oil over medium-high heat until the moisture has evaporated and the mushrooms are soft, fragrant, and starting to brown, about 5 minutes. Stir the mushrooms into the nut loaf mixture and proceed with the recipe.
VARIATION: Stuffed Peppers: My lovely sister-in-law devised this healthy variation made without the puff pastry: “I made the nut and bean loaf, then added 1/4 cup of tomato sauce. I stuffed it into seven cleaned-out medium green bell peppers and baked them at 350°F for 30 minutes. They tasted great, travel nicely (I took one to work), and are very filling! While I was stuffing the peppers, I noticed that (for me) cutting a slit down one of the sides is helpful in stuffing the pepper, but you might be better at stuffing than I am.” Thanks, Rachel!