Marinate the Steak: In a large resealable bag, mix together the skirt steak, 3 tablespoons of olive oil, lime juice, orange juice, minced garlic, chopped oregano, bay leaves, ground cumin, cayenne pepper, and a pinch of salt and pepper. Seal the bag tightly and shake to ensure the marinade fully coats the steak. Let it marinate in the refrigerator for at least 30 minutes or overnight for deeper flavor.
Preheat the Oven: Set your oven to 450°F and position the rack in the upper third of the oven to prepare for roasting.
Prepare the Vegetables: On a large baking sheet, combine the cubed potatoes, sliced onion, and bell pepper with the remaining 1 tablespoon of olive oil. Add a generous pinch of salt and pepper, tossing to coat everything evenly. Spread the vegetables out in a single layer and roast for approximately 20 minutes, or until they begin to turn golden.
Cook the Steak: Once the vegetables are partially cooked, remove the steak from the marinade, allowing any excess liquid to drip off, and discard the marinade. Push the roasted vegetables to the edges of the baking sheet to make room for the steak. Place the steak in the center of the baking sheet and return it to the oven. Switch to the broil setting and cook for 5 minutes. Flip the steak, stir the vegetables, and broil for an additional 6 minutes, or until the steak reaches your preferred level of doneness. Let the steak rest for 5 to 10 minutes before slicing.
Prepare the Chimichurri: In a medium-sized bowl, combine the chopped cilantro, diced mango, Fresno pepper, red wine vinegar, olive oil, and lime juice. Stir the mixture well, then gently fold in the diced avocado, being careful not to mash it.
Serve and Enjoy: Slice the steak against the grain into thin strips. Serve it alongside the roasted vegetables, topped generously with the avocado chimichurri. Leftovers can be stored in an airtight container in the refrigerator for up to three days.