BOIL: Bring the water, vinegar, salt, sugar, bay leaves, black peppercorns, and oregano to a boil in a medium saucepan.
SIMMER: Once boiling, add the sliced carrots, onions, sliced jalapeños, Serrano, and garlic and let it simmer in the vinegar mixture for 2-3 minutes over medium heat so that they just simmer.
COOL: Remove the saucepan from heat, and allow the veggies for cool for 5 minutes in the vinegar.
TRANSFER: Then carefully transfer the pickled veggies to a clean jar using tongs. Carefully pour the liquid over the veggies and ensure they are all submerged.
STORE: The pickled carrots are ready to use at this point, but they do taste better once the carrots have sat for a few hours in the vinegar mixture and cooled down. Refrigerate for up to 1 month.