In a large pot, bring the vinegar, water, garlic, peppercorns, oregano, bay leaves, and salt to a boil. Once boiling, lower temperature to simmer.
Peel carrots and slice on the diagonal into long coins. Slice the jalapeños into rings (remove seeds for a more mild flavor), and largely cut the onion into large slices.
Add the carrots, onion, and jalapeños to the pot, and cook on low for 15 minutes uncovered, until the carrots begin to soften but still have a nice crunch. Remove the pot from heat and let the carrots cool on the stove top. Once cool, store in a jar or airtight container in the fridge for up to 2 weeks.
Notes
Just a note: this is a fresh refrigerator carrots recipe, and not a canning recipe for long-term storage. These carrots will last 2 weeks (although they go much quicker)! If you are looking for a canning recipe, you can find a ton in this great Ball canning guide.