In a medium bowl, whisk together olive oil, lime juice, minced garlic, cumin, chili powder, salt, and pepper until well combined. Add the flank steak and coat well. Cover and marinate for at least 30 minutes, or refrigerate for up to 2 hours.

Preheat your grill or skillet over medium-high heat. Cook the marinated flank steak for 4-6 minutes on each side until desired doneness. Transfer to a cutting board to rest.

In a separate bowl, combine diced tomatoes, red onion, jalapeño, a squeeze of lime juice, and salt to create salsa. Mix well and let sit for 10 minutes.

Lay tostada shells on a platter. Layer with sliced carne asada, followed by shredded lettuce, avocado slices, and salsa. Sprinkle with chopped cilantro.

Serve with lime wedges for an extra burst of flavor.