Grate the zucchini into a large bowl and toss with the 1 teaspoon salt. Let it sit for 15 minutes so the salt draws out the moisture.
Meanwhile, stir together the ground flaxseed, water, and lemon juice in a small bowl. Let it sit for 5 minutes, until thickened and gel-like.
Transfer the salted zucchini to a fine-mesh strainer and press firmly with your hands to squeeze out as much liquid as possible. The drier it is, the better your fritters will hold together.
Return the zucchini to the large bowl and add the flax mixture, all-purpose flour, baking powder, scallions, garlic, dill, mint, vegan feta, and black pepper. Stir until just combined into a thick, messy batter. Taste and adjust salt as you like.
Heat the oil in a large skillet or dutch oven over medium-high heat. After 90 seconds when the oil is hot, working in batches, drop 2-3 tablespoon dollops of the batter into the skillet, flattening each slightly with the back of a spoon. Don't overcrowd the pan. Fry for 3 to 4 minutes per side, until deep golden brown and crisp at the edges. Adjust the heat down if they're browning too fast before cooking through.
Transfer the fritters to a wire rack suspended over a baking pan to drain and cool slightly. Repeat with the remaining batter, adding more oil to the skillet as needed.
For the optional yogurt dipping sauce, mix together the yogurt, lemon juice, garlic, dried mint, salt and olive oil in a small bowl using the tines of a fork.
Serve the mukver warm with garlic yogurt on the side, optionally with a squeeze of lemon juice or chopped fresh parsley.