In a medium bowl, whisk together fresh lime juice, chili powder, garlic powder, salt, and pepper until well combined. Place the flank steak into the marinade, ensuring it’s fully coated. Cover and refrigerate for at least 2 hours, ideally up to 8 hours.

While the steak marinates, prepare the avocado salsa by dicing ripe avocados and chopping a jalapeño or serrano pepper. In a mixing bowl, combine the avocado, chopped pepper, and freshly chopped cilantro. Stir gently to combine.

Preheat your grill to medium-high heat, about 400°F (200°C). Remove the marinated flank steak from the refrigerator and let it sit at room temperature for about 15 minutes before grilling.

Place the steak on the hot grill and cook for approximately 5-6 minutes per side, aiming for a perfectly charred exterior while achieving medium-rare doneness (135°F/57°C internal temperature).

After grilling, remove the steak from the grill and let it rest for at least 5 minutes.

Once rested, slice the steak against the grain into thin strips and serve topped with the fresh avocado salsa.