Make Lime Pickled Onions first and macerate while you make the tacos.

Preheat the oven to 425ºF. Arrange a rack in the top third and the bottom of the oven.

Heat a large frying pan over medium-low heat for a minute or two, then add the walnuts to toast. Toss frequently to prevent burning, until golden brown in spots and nutty in aroma, about 5 minutes.

Meanwhile, drain and rinse the black beans. Add to a dish towel and pat dry as well as you can. It’s okay if you smush them.

Stir together all the ingredients for the Taco Spices. Set aside.

Add the toasted walnuts to a food processor. Blend for a few seconds until in fine crumbs, but don’t over-process into a paste.

Add the mushrooms, nutritional yeast, and mushroom powder. Blend for a few seconds, followed by just a few pulses until mushrooms are finely chopped.

Add in the black beans and do 10 quick pulses to break them up but leave some beans intact. The mixture should be a bit moist but not sticky.

Return the frying pan to medium heat and heat for 1 minute, then add 3 tablespoons of oil. Once warm, add the garlic. Stir frequently until just turning color, 2 to 3 minutes (do not brown).

Add the Taco Spices and stir constantly for 20 to 30 seconds.

Add the bean-mushroom mixture and toss well to coat it in the spiced oil. Cook, stirring occasionally, for 5 to 7 minutes. If it starts to stick, deglaze with a splash of water.

Reduce the heat to medium-low. Stir in the salsa, using the liquid to deglaze any browned bits. Cook for 1 minute until thick and spreadable. Remove from the heat and season to taste with salt.

Spread approximately ¼ cup of the bean mixture onto one side of each tortilla. Sprinkle with a layer of cheese, then fold the tortilla over onto the side with the filling and press down on the edges to seal.

Add 1 tablespoon of oil to a large rimmed sheet pan, using a pastry brush to spread it out. Arrange the tacos without overlap, gently spreading them into the oil. Now brush the top sides of the tacos with a light layer of oil.

Bake on the bottom rack for 8 to 12 minutes, or until crispy and golden brown on top.

Remove from the oven and flip the tacos. Bake on the top third rack for 5 minutes, or until crispy and golden brown on the bottom.

Allow to cool a bit, as they will be very hot. Then carefully pry open the tacos and dollop with Chipotle Crema (or Avocado Crema), Lime Pickled Onions, and shredded lettuce. Serve leftover crema on the side for dipping.