Roast the Peppers. Preheat the broiler, then lightly rub the poblano peppers with a little oil and place on a baking sheet. Roast, turning as the pepper skin blackens and chars, until fully roasted all over, 6-8 minutes total. Remove and immediately place in a bowl and cover tightly with wrap or a kitchen towel to steam, this will make the skins easier to remove. When cool enough to handle, gently peel away the skin, discard the stem and seeds and slice into thin strips.

Cook the Potatoes. While the peppers are cooking, place the potatoes in a pot and cover with a few inches of water. Bring to a boil, then reduce heat to low and cook for 10 minutes, or until just fork tender. Drain and set aside.

Make the tacos. Heat the remaining oil in a large skillet over medium heat and add the mushrooms, onions and a pinch of salt. Cook for 10 minutes, until mushrooms are browned and onion is cooked down. Add in the drained potatoes and peppers along with the cumin and cook another 5 minutes, until potatoes are crispy and mixture is warmed together.

Make the sauce. While the tacos are cooking, place the cilantro/parsley, water, garlic, lime juice, salt and pepper in the base of a food processor or blender and pulse 5-6 times until coarsely chopped. Add in the olive oil and pulse again, 8-10 times until cilantro/parsley is finely chopped, but some texture remains. Season to taste, adding in more salt/pepper as desired.

Assemble! Warm the tortillas in the microwave or in a dry skillet, then fill with mushroom and potato filling and drizzle with sauce.