Prepare the Vegetables
Wash zucchini thoroughly and slice into rounds or spears.
Thinly slice onion and smash garlic cloves.
Pack the Jars
In a clean quart-sized jar (or 2 pint-sized jars), layer zucchini, onion slices, garlic, dill, mustard seeds, peppercorns, and red pepper flakes.
Make the Brine
In a small saucepan, combine vinegar, water, sugar, and salt.
Bring to a boil, stirring until sugar and salt dissolve.
Remove from heat.
Fill the Jars
Carefully pour the hot brine over the zucchini mixture, leaving about ½ inch of headspace at the top.
Tap the jar gently to release any air bubbles.
Seal and Chill
Screw on lids tightly.
Let jars cool to room temperature before placing them in the refrigerator.
Marinate and Serve
Allow pickles to chill for at least 24 hours before eating for the best flavor.
Enjoy within 2–3 weeks for peak freshness.