Preheat 2 tablespoons of oil to medium heat for a few minutes in a large skillet. Add the potatoes, cover and cook for 15 to 20 minutes. Stir them as needed to brown most sides. Drain onto plate lined with paper towels, set aside.
To that same skillet, add 1 more tablespoon of olive oil and return to medium heat. Add onion, bell pepper, serrano and garlic. Season lightly with salt and pepper and sauté for 5 minutes. Add the mushrooms and sauté for another 5 minutes. Stir in the diced Roma tomato and cook for 10 minutes or until tomatoes begin to soften and reduce slightly.
In the blender, add the remaining tomato, chicken bouillon, oregano, cumin, pepper and 1 c of water. Blend on high until smooth add to pan, stir well to combine. Bring to a boil, taste for salt and cook for 5 minutes or until the sauce thickens. Add the green chile, nopalitos and fried potatoes. Stir well to combine. Taste for salt. Continue cooking for 5 minutes. Cover and remove from heat.
Brush the tortillas with oil on both sides. Warm on preheated griddle as tortillas get warm and start to soften, fill them with mushroom/potato filling and fold over. Continue cooking them, turning as needed until crispy on both sides. Transfer to serving dish, garnish with your favorite toppings.