To prepare the marinade, first juice the limes into a small, shallow dish.
Mince the garlic and cut the jalapeno into small dice. Depending on how much heat you like, you may want to use only 1/2 of the jalapeno and/or remove the ribs and seeds from the inside. Add the garlic and diced jalapeno to the lime juice along with the salt. Stir to combine.
Peel and cut the onion in half vertically. Slice the onion vertically into thin strips. Set aside.
Note: It is important to use very fresh scallops for this dish as they will be eaten raw.
To prepare the scallops, first remove the tough muscle from the side (if present) and discard.
Slice the scallops horizontally, into thin, even pieces. Once done, transfer to the marinade, along with the sliced red onions. Toss to combine.
Cover and transfer to the refrigerator. Let marinate for approximately 30 minutes to 1 hour or just until opaque.
Do not remove the scallops from the refrigerator until you are ready to eat them. For food safety reasons, shellfish must be kept as cold as possible. You can even place the serving dish over a bed of ice to ensure the seafood is kept very cold. Serve with plain crackers, if desired.