How to Make It
Place sirloin steaks in a large ziplock plastic freezer bag. Process white onions, garlic cloves, seeded and chopped jalapeños, kosher salt, black pepper, beer, and water in a blender until smooth. Pour over steaks; seal bag, and turn to coat. Chill 3 hours.
Preheat grill to medium-high (about 450°F). Remove steak from marinade; discard marinade. Place steak on oiled grates, and grill sirloin, uncovered, until a thermometer inserted in thickest portion registers 145°F or to desired degree of doneness, 5 to 6 minutes per side for medium-rare. Let steak stand 3 minutes before diagonally slicing across the grain.
Toss together cilantro leaves and red onion slices. Heat tortillas on a comal (flat griddle) or according to package directions.
Divide steak among tortillas; top with cilantro mixture. Serve with limes and salsa.
To give the Grilled Sirloin Tacos an extra kick of heat, Hernandez suggests dipping the cut sides of fresh lime slices in ground chile powder.