1. Slice off the stems of the jalapeños and cut them into rounds slightly shy of 1/4-inch (.5cm). Peel the carrot and cut it into 1/4-inch (.5cm) slices. Peel the onion and cut it in half. (Reserve the other half for another use. Slice the onion into 1/4-inch (.5cm) slices.
2. Heat the vinegar in a nonreactive saucepan with the water, garlic clove, salt, sugar, oregano, peppercorns, and bay leaf until simmering, and the salt and sugar are dissolved.
3. Add the jalapeños, carrots, and onions. Let cook in the pan for 1 minute, then cover, remove from heat, and let stand 15 minutes.
4. Ladle the mixture into jars, close them, and refrigerate until ready to serve.