01 - Whisk together olive oil, lime juice, garlic, cumin, chili powder, smoked paprika, salt, and black pepper in a bowl. Add the beef slices and toss to coat evenly. Marinate for at least 15 minutes, up to 2 hours refrigerated for optimal flavor development.
02 - Place a large skillet or cast-iron pan over medium-high heat. Add a small drizzle of oil if the pan appears dry.
03 - Arrange the marinated beef in a single layer across the hot pan. Sear for 2-3 minutes per side until browned and just cooked through. Transfer beef to a plate and keep warm.
04 - In the same pan, add the sliced bell peppers and onion. Sauté for 5-7 minutes, stirring occasionally, until vegetables are softened and slightly charred.
05 - Return the cooked beef to the skillet with the vegetables. Toss everything together to combine and heat through for 1-2 minutes.
06 - Heat tortillas in a dry skillet for 30 seconds per side or wrap in damp paper towels and microwave for 30 seconds until warm and pliable.
07 - Spoon the beef and vegetable mixture into warm tortillas. Garnish with fresh cilantro, a squeeze of lime juice, and your choice of toppings. Serve immediately while hot.