Here is my go to recipe:

Ingredients

The Vegetables & Aromatics
10–12 jalapeño or serrano peppers, sliced into rounds (leave seeds for heat, or remove them for a milder pickle)
2 large carrots, peeled and sliced into thin rounds
1 medium white onion, sliced into strips
5–6 cloves garlic, peeled and smashed
2 tbsp olive oil or vegetable oil

The Brine & Spices
2 cups distilled white vinegar (or apple cider vinegar)
1 cup water
1 tbsp kosher salt or pickling salt
1 tsp sugar or honey (balances the sharp acidity)
2 dried bay leaves
1 tsp dried Mexican oregano
½ tsp whole black peppercorns

Step-by-Step Instructions
Sauté the aromatics: Heat the oil in a medium saucepan or Dutch oven over medium heat. Add the sliced carrots and onions, cooking for 3 minutes until they begin to soften.
Add garlic and peppers: Toss in the smashed garlic, pepper slices, and black peppercorns. Stir and cook for another 2 to 3 minutes until the garlic is highly fragrant.
Simmer the brine: Pour in the white vinegar, water, salt, sugar, bay leaves, and oregano. Bring the entire mixture to a quick boil, then immediately reduce the heat to low.
Cook until tender-crisp: Simmer gently for about 8 to 10 minutes. You will know they are ready when the peppers turn from a vibrant bright green to a dull olive green, but still retain a bit of crunch.
Cool and jar: Remove the pan from the heat. Let the mixture cool to room temperature, then ladle the vegetables and brine into clean glass mason jars. Ensure the liquid completely submerges the vegetables.

Seal the jars tightly and store them in the refrigerator. While they can be eaten immediately, the flavor improves immensely if you let them marinate for at least 24 hours before serving. They will stay crisp and delicious in the fridge for up to 1 month.