Prepare the vegetables by washing and finely chopping zucchini, tomatoes, onion, and green bell peppers. Set aside in a bowl.

In a pot, heat olive oil over medium heat, add chopped vegetables and minced garlic. Sauté for about 10 minutes until softened.

Stir in vinegar, sugar, salt, cumin, red pepper flakes, and black pepper. Bring to a boil while stirring occasionally.

Lower heat and let the mixture simmer for 20-25 minutes until thickened.

Remove from heat, incorporate fresh cilantro if using, and stir well.

Ladle hot salsa into sterilized jars, leaving 1/2 inch of headspace. Clean jar rims and seal tightly.

Process jars in boiling water for 15 minutes, ensuring they are covered by at least 1 inch of water.

Cool jars undisturbed for 12-24 hours and check seals before storage.