In a blender or food processor, combine all of the tzatziki ingredients. Blend until smooth. Refrigerate until ready to use.
Place the grated zucchini in a fine mesh strainer over a bowl. Sprinkle with 1 teaspoon salt to draw out the liquid and let sit for 10-15 minutes. Then, wring all of the liquid out using your hands and set aside.
In a large bowl, combine the zucchini, spinach, feta, herbs, eggs, scallions, and garlic. Stir to mix well. Then, sprinkle in the flour and baking powder, a bit at a time, until it all is incorporated and holding together.
Heat about ¼ cup olive oil in a skillet over medium heat. Once warmed, drop 3 scoops of batter into the skillet. (Aim for about 3 tablespoons worth of batter, each) After about 30 seconds, flatten them out a by pressing them down gently with a spatula. Pan fry for about 3 minutes, and then flip to fry the other side for an additional 3 minutes, or until golden brown.
Place the fritters on a paper towel lined plate to absorb excess oil, and serve warm with the Garlic.