Place steak in a large, resealable plastic bag, and add oils and vinegar; season generously with the salt, pepper, and Mexican oregano, if using. Roughly chop the cilantro stems and add them to the marinade, reserving the leaves for later. Add garlic and jalapenos, seal bag, and shake to coat and combine. Marinate in the refrigerator for at least 2 hours.
Remove meat from the fridge and allow it to come to room temperature while you prepare a grill pan or charcoal grill for medium-high heat. Brush grill with olive oil -- if using a grill pan, consider using Harvest Olive Wood-Smoked Olive Oil to reinforce the smokiness of a charcoal cookout -- and remove steak from marinade, making sure to brush off any solid bits that may burn. Discard marinade. Cook steak to desired doneness, turning once (roughly 4 minutes a side for medium-rare). Remove meat to a cutting board, tent loosely with foil, and allow to rest for 10 minutes before slicing against the grain into 1/4-inch slices and serving, garnishing with chopped cilantro.
Serving suggestions: This citrusy steak is wonderful with white rice or in a zesty sandwhich; it also makes a great soup (recipe here), though you may want to shave a minute off each side of the grill time. The steak will continue to cook while it simmers.
Note: Mexican oregano is worth seeking out and keeping on hand if you cook Mexican-inspired dishes with any regularity. It's stronger and fruitier than its more common Mediterranean counterpart, and its lemony undertones work especially well in this classically citrusy marinade. Most large supermarkets should carry it in their Mexican or otherwise "ethnic" aisles.
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