Step 1

Combine onion, cilantro, lime juice, soy sauce, olive oil, brown sugar, oregano, red pepper flakes, and garlic in a large bowl.

Step 2

Place steak in a baking pan and pour marinade on top. Cover and refrigerate at least 1 to 4 hours.

Step 3

Preheat an outdoor grill for high heat and lightly oil the grate.

Step 4

Grill steak 2 to 4 minutes per side, to desired doneness. Allow meat to rest 5 to 10 minutes before slicing against the grain into 1/4-inch slices.

Step 5

Add meat to tortillas and top with your favorite toppings.