Season sliced meat with salt, black pepper, and crushed red pepper. Squeeze lime juice over meat. Turn until evenly coated. Cover, and refrigerate for 30 minutes. OR: The night before, place the meat in a plastic bag. Cover with the juice of the lime and the lemon plus enough water to cover (you can use use coke or 7-up instead of water if you prefer). Add salt, pepper and red pepper then seal and allow to marinate overnight.
Combine tomatillo and jalapeno. Puree in a blender for 15 to 20 seconds until thick.
Heat 1 tablespoon oil in a large skillet over medium high heat. Pour in tomatillo mixture. Stir frequently for 5 minutes. Add in beef broth. Stir to mix thoroughly then reduce heat, and simmer for 20 to 30 minutes. Transfer to a serving dish when it will coat a spoon.
Again, heat 1 tablespoon oil in a large skillet. This time over high heat. Stir in about 1/3 of the beef, and sauté for 1 minute. Transfer to serving dish. Repeat with remaining beef.
Meanwhile, heat tortillas in the oven. I find that placing as many as possible flat on a cookie sheet under the broiler for 2-3 minutes works well. Your oven will be unique, watch them closely.
To serve, add desired amount of meat to a tortilla and spoon over some tomatillo mixture. Top with onions, tomatoes, avocado and cilantro. A bit of shredded cheese works well too. You may want to double up tortillas or serve in crunchy taco shells.