Step 1: Prepare the Beef Filling

1. Heat olive oil in a skillet over medium heat. Add the diced onion and garlic, sauté until fragrant and softened.
2. Add the ground beef or sliced flank steak to the skillet. Cook until browned, breaking up the meat with a wooden spoon if using ground beef.
3. Stir in chili powder, cumin, paprika, oregano, salt, and pepper. Mix well to coat the beef evenly with the spices.
4. If the mixture seems dry, add ¼ cup of beef broth or water for extra moisture. Let it simmer for 2-3 minutes, then set aside.

Step 2: Make the Salsa

1. In a bowl, combine diced tomatoes, chopped onion, jalapeño, cilantro, lime juice, and salt.
2. Mix well and let it sit for 10-15 minutes to allow the flavors to meld.

Step 3: Prepare the Guacamole

1. Scoop the avocado flesh into a bowl and mash it with a fork until smooth or slightly chunky, based on preference.
2. Mix in lime juice, minced garlic, diced tomato (if using), cilantro, and salt. Taste and adjust seasoning as needed.

Step 4: Warm the Tortillas

1. Heat the tortillas in a dry skillet over medium heat for 15-30 seconds per side, or wrap them in foil and warm in the oven at 350°F (175°C) for 10 minutes.

Step 5: Assemble the Tacos

1. Lay a warm tortilla on a plate. Add a spoonful of beef filling as the base.
2. Top with a scoop of fresh salsa and guacamole.
3. Add optional toppings like shredded lettuce, cheese, or a squeeze of lime juice for extra flavor.

Step 6: Serve and Enjoy

1. Serve immediately with lime wedges on the side. Pair with your favorite sides like Mexican rice, refried beans, or elote.