Ask your butcher to cut the baby back rib racks in half, making them half their width. Once at home, remove their back membrane. Cut them into pieces with 3 ribs per piece and place them in a bowl.
Make the marinade: In the jar of a blender, add the lime juice, vinegar, oil, garlic, dried piquín, oregano, salt, and pepper. Puree until completely smooth.
Pour the marinade over the ribs and toss to coat. Cover with plastic wrap and place in the refrigerator anywhere from 2 to 24 hours.
When ready to cook, remove the ribs from the refrigerator. Preheat your grill to medium. Brush the grill grates clean with a large piece of white onion.
Place the ribs in 3 to 4 large pieces of aluminum foil, in a single layer and seal the tops tightly, making flat packets. Place them over direct heat and cook for 1 hour, flipping the packets over once in between.
Remove the packets from the grill, open them up, and place the ribs directly on the grates, bone sides down first. Grill for about 4 to 5 more minutes per side, with the lid closed, until they char and brown for a delicious crunch along the edges.
Serve with the Green Piquín Chile and Oregano Salsa on the side, to dip the ribs as you eat them.