Rinse all your fresh vegetables under cold water. Cut the cauliflower into small florets, slice the carrots and celery, and chop the red bell pepper into strips.
In a large pot, combine the water, white vinegar, salt, and sugar. Bring this mixture to a boil over medium-high heat, stirring until fully dissolved.
Once boiling, add the smashed garlic, bay leaves, serrano chiles, oregano, celery seeds, fennel seeds, and yellow mustard seeds. Simmer for about 5 minutes.
Carefully add the cauliflower, carrots, celery, and red bell pepper to the brine. Cook for about 2-3 minutes to slightly soften the vegetables.
Using a slotted spoon, transfer the blanched vegetables into clean glass jars, packing them tightly.
Ladle the hot brine over the packed vegetables, ensuring they are fully submerged.
Seal the jars tightly with lids and let them cool to room temperature before refrigerating. For best results, let sit for at least 24 hours.