Preparing the Grilled Beef

1. Marinate the Beef: In a medium bowl, combine the olive oil, lime juice, minced garlic, ground cumin, smoked paprika, salt, and pepper. Place the flank steak in a shallow dish or a resealable plastic bag. Pour the marinade over the steak, ensuring it’s well coated. Cover or seal and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
2. Preheat the Grill: Preheat your grill to high heat. If using a grill pan, heat it over medium-high heat.
3. Grill the Steak: Remove the steak from the marinade and let it sit at room temperature for about 5 minutes. Place the steak on the grill. Cook for 4-5 minutes per side for medium-rare, or until the desired doneness is reached.
4. Rest and Slice: Remove the steak from the grill and let it rest for 5-10 minutes. This allows the juices to redistribute throughout the meat. Slice the steak thinly against the grain.

Making the Chipotle Sauce

5. Combine Ingredients: In a small bowl, mix together the chopped chipotle peppers, sour cream, lime juice, minced garlic, and salt until well combined. Adjust seasoning to taste.

Preparing the Salsa

6. Mix the Salsa: In another bowl, combine the diced tomatoes, red onion, cilantro, lime juice, salt, and pepper. Toss to mix all ingredients thoroughly.

Assembling the Tacos

7. Warm the Tortillas: Heat the tortillas on the grill or in a dry skillet over medium heat for about 30 seconds on each side, until warm and pliable.
8. Assemble Tacos: Place a few slices of grilled beef on each tortilla. Drizzle with chipotle sauce, then top with fresh salsa. Add avocado slices and crumbled cheese if desired.