Grate the zucchini, carrots, and potatoes and place them into a colander to strain.
Heat 1 tablespoon olive oil in a large skillet and add the diced yellow onions and diced green onions. Cook until tender, about 4-5 minutes.
Squeeze the grated vegetables thoroughly to remove excess liquid. Place into a large bowl and mix in the beaten eggs, crumbled feta cheese, fresh herbs, and the cooked onion mixture. Stir until combined. Add the flour, salt, and pepper and stir well.
Using an ice cream scoop or large cookie scoop, scoop the mixture and form it into balls. Place onto a baking sheet until ready to cook.
Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Add the zucchini fritters and cook until golden. Flip and cook the other side until golden. Remove the fritters from the pan and place on a paper towel-lined plate or baking sheet to absorb the excess oil. Repeat until all the fritters are cooked.