Combine the avocado, mango, lime juice, minced serrano, and minced red onion in a bowl. Season with a generous pinch of salt and stir to combine. Taste and add more salt if needed. Transfer to the refrigerator.

Preheat oven to 425ºF.

Place the diced potatoes, baking soda, and salt in a large pot. Cover with water by 1 inch and bring to a boil. Cook for 10 minutes until just slightly under fork-tender. Drain into a large bowl.

Using tongs, transfer the potatoes to a baking sheet in an even layer. Let stand for 5–10 minutes.

Transfer the potatoes to a bowl with the extra virgin olive oil, ancho chili powder, paprika, and cayenne powder. Taste and add more salt, if needed. Toss to coat. Return to the baking sheet in an even layer and roast for 20–30 minutes until golden brown.

Wipe out the bowl you used to season the potatoes and add lime juice, minced cilantro, and minced serrano pepper.

Carefully add the roasted potatoes to the bowl and toss to coat. Taste and season once more with salt and pepper if needed. Transfer to a serving bowl.

Place a skillet on the stovetop over medium-high heat. Add a scant amount of neutral oil and use a paper towel to brush it into an even layer. The skillet should be slick but not pooling oil anywhere.

Pat the steak dry and season with salt, pepper, and chili powder.

Turn the heat on the skillet to high. Let it continue to heat for 1–2 minutes. Add the steak and cook without moving for 3–4 minutes. Flip and continue cooking, adjusting the heat if needed until it reaches your desired internal temperature. Skirt steak only needs to cook for 3–4 minutes per side, depending on how thick it is. Transfer it to a plate and cover with foil to rest for 5–10 minutes.

Return the heat on the skillet to medium-high. Add another drizzle of neutral oil and let it heat for 1 minute. Once hot and shimmering, add the sliced peppers and onion. Cook, turning occasionally, for 5 minutes until tender-crisp and charred in spots. Season with salt and pepper. Transfer to one side of a serving platter.

Transfer the steak to a cutting board and slice thinly against the grain. Transfer to the other side of the serving platter with the cooked peppers.

Pile the steak and peppers into warm tortillas with shredded lettuce. Spoon the mango-avocado salsa on top. Serve the warm roasted potatoes on the side. Enjoy!