Dividing equally, put the peppercorns and garlic into the clean glass jars. Add the dried onion if you’re using that. Pack the shrimp into the two jars, adding raw onion and lime slices as you go.
In a small saucepan, combine the vinegar, lime juice, ginger, sugar, and salt. Bring to a boil and stir until everything is dissolved. Immediately pour the hot liquid over the shrimp leaving ¾-inch headspace. Everything in the jar should be submerged.
Tap the jars on the counter and/or poke around the edges with a skewer to release any air bubbles. Add a little more hot liquid if needed.
To make the jar airtight, you are going to float oil on the top of the liquid like this: using a dinner spoon, lay the spoon--back side up--against the inside rim of the jar and just touching the surface of the pickling liquid. Carefully pour the oil in a slow, thin, stream over the back of the spoon. This will allow the oil to spread over the surface of the liquid.
Carefully screw down the jar lids and put the jars in the refrigerator. Let sit undisturbed for 24 to 48 hours. These will keep two or three weeks in your fridge unless you eat them all first.