Line 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 ready.
Chop walnut (food processor makes it easy) into very small bits. Scrape into large bowl.
Chop brown rice and chickpeas in food processor until mixture forms a coarse mash. Add this to the mixing bowl along with oat bran, spices, soy sauce, mustard and peanut butter. Knead together until it holds its shape.
Unfold the first sheet of puff pastry and roll into a 12x12 square. Cut into six rectangles about 6x4.
Scoop up a handful of the nut loaf mixture and form it into a small rectangular loaf (about 3x1x3/4 inches). Place in the center of a puff pastry. Dip your fingers in the water and lightly wet the top of the loaf.
Fold the short ends of the pastry over the loaf, then fold up the long edges using some water to seal it shut.
Place the mini Wellington seam side down on the prepared baking sheet. Repeat with the other 5.
Bake at 400F for 25 minutes. The crust should be puffed and golden and the inside heated through.
The Wellingtons can be made ahead and refrigerated until it's time to bake.