In a mixing bowl, add the vinegar, water, garlic, peppercorns, salt, pure maple syrup, and the juice of one lime. Mix to incorporate well. Set aside.
Thin-slice the onions. Place the sliced onions into the jar, stacking them flat one by one.
Pour the seasoned vinegar into the jar with the onions. Put on the lid and give it a shake.
Store into the fridge for a minimum of 2 hours before enjoying.
Notes
This makes enough to fill a one-pint jar. Note: if you do not uniformly stack them flat, one by one, you cannot fit two medium onions. If you prefer to separate the rings, you can fit one medium size onion.