Pat the cubed top sirloin dry on a cutting board, then evenly season with chili powder, ancho chili powder, Knorr granulated beef bouillon, garlic powder, onion powder, ground cumin, brown sugar, 3/4 teaspoon salt, dried oregano, smoked paprika, ground coriander, and optional cayenne; set aside to rest 20–60 minutes.
While the steak rests, warm and prepare your toppings and tortillas; keep tortillas warm using your preferred method (skillet, broiler, microwave, or oven).
Heat 2 tablespoons vegetable oil in a large cast iron skillet over medium-high heat until shimmering.
Add half the steak to the hot skillet and sear 1–2 minutes, then stir and continue cooking just until browned but still juicy (about 1–2 more minutes); season to taste with additional salt or cayenne if desired. Transfer to a plate and repeat with the remaining steak.
Assemble tacos by piling cooked steak into warmed tortillas and adding desired toppings such as cilantro, pickled red onions, pomegranate arils, Cotija cheese, sour cream, avocado crema, guacamole, or salsas.