In a small container combine: 1T chili powder, 1tsp oregano, 1tsp cumin, 1/2tsp garlic powder & 1tsp salt.
Slice beef into thin slices, and then chop into bite-sized pieces. Place into a medium bowl.
Rub seasoning mix into chopped chuck roast in a medium bowl. Add juice of 2 limes and allow to marinate ~1 hour.
Slice 2 avocados into slices.
Grate ~1/2c cotija cheese.
Heat a large saute pan over medium heat. Add chopped beef & marinade and cook, stirring, ~5-6 mins or until cooked through.
Place 8 corn tortillas on a griddle or pan over medium-low heat until pliable.
Build tacos: tortilla + beef + shredded lettuce + avocados + pickled jalapenos (optional) + 1-2T cotija cheese.