Place 1 cup unsalted cashews in a bowl and add enough cold water to cover.
Let the cashews soak for at least 6 hours in the fridge (or overnight).
Drain and discard the soaking liquid, reserving the cashews.
Preheat the oven to 400 degrees Fahrenheit.
Slice 2 medium poblano peppers in half lengthwise, then remove and discard the stems and seeds.
Add the poblano peppers and 1 tablespoon extra virgin olive oil to a sheet pan, then use your hands to evenly coat them with oil.
Bake for 20-25 minutes or until tender and blistered.
Add 1 cup cold water, the roasted poblano peppers, soaked and drained cashews, 1 garlic clove, 1/3 cup nutritional yeast, 1 tablespoon tapioca starch, 2 tablespoons fresh lime juice, and 3/4 teaspoon salt to a high-powered blender.
Blend until smooth and creamy.
Add 2 cups rinsed and drained canned black beans to a mixing bowl along with 1/2 cup of the blended poblano sauce mixture.
Use a potato masher or the back of a fork to mash the beans and mix with the sauce. No need to get them completely smooth—some chunks are fine.
Spoon about 1/4 cup of the mashed bean mixture onto each tortilla (use 8 medium (6 to 7-inch) corn tortillas, then roll up tightly.
Place the rolled tortillas seam-side down in a lightly greased 9 x 13-inch baking dish.
Pour the rest of the poblano sauce on top of the rolled tortillas.
Cover the baking dish with a lid or aluminum foil, then bake for 20 minutes or until heated through.
Garnish with chopped green onions or cilantro, if desired.