Bring a pot of water with potatoes to the boil. Cook until potatoes can be easily pierced with a paring knife. Do not over-cook or they will be mushy. Cool potatoes.

Sauté red onion, in a large sauté pan, lightly coated with evoo, over medium-high heat, until caramelized and dark brown. Slice cooked potatoes thinly and add them to the pan. You may need to add more evoo. Cook, stirring occasionally until potatoes are crispy and golden.

Add mushrooms and stems. You may need to add a little more evoo, and continue cooking until browned and softened. Add garlic and continue cooking for 2-3 minutes until garlic has softened.

Transfer filling to a bowl and keep warm.

Chipotle Mayo:

Mix mayo, chipotle and lime juice in a small bowl.

To Assemble the Tacos:

Preheat oven to 250°F

Wrap tortillas in foil and heat in oven for 10 minutes and keep warm.

Arrange filling, salsa, cheese, guacamole, chipotle mayo in separate bowls and serve.