For the Seasoning: Combine all ingredients together in a small bowl and set aside
For the Chimichurri Sauce: Combine all ingredients together in a small bowl and mix until merged.
For the Steak: Add 1 tablespoon of olive oil to a plate along with 2 tablespoons of the seasoning blend and mix together. Next add the flank steak and coat on all sides with the olive oil-seasoning blend and let marinate for at least 20 minutes.
In a large saute pan on high heat with 1 tablespoon of olive oil, add the onions and caramelize. Once brown remove them from the pan.
In the same pan on high heat, add in the marinated flank steak and sear on both both sides for 3 minutes or until golden brown and a medium-rare internal temperature is achieved.
Let the meat rest on a cutting board for 2 to 3 minutes before thinly slicing against the grain.
To plate: Place a small amount of the sliced flank steak inside of a corn tortilla shell and top off with 1 tablespoon of chimichurri sauce, caramelized onions, sliced avocado and queso fresco. Garnish with limes.