Place a rimmed baking sheet in oven; preheat to 200°F. Place zucchini in a sieve over a bowl and sprinkle with 1/2 tsp. salt. Let stand 10 minutes. Using a clean kitchen towel, squeeze out as much liquid as possible from zucchini. Discard liquid from bowl and wipe out with a paper towel. Add flour and eggs to bowl. Whisk until combined. Gently but thoroughly stir in zucchini and scallions.
Warm oil in a large skillet over medium-high heat until shimmering. Working in batches, add heaping 1-Tbsp. mounds of batter to skillet, spacing fritters so they don't touch. Cook until golden brown and crisp, 2 to 3 minutes per side. Sprinkle with salt and remove to baking sheet in oven.
Repeat with remaining batter, adding more oil to skillet if necessary between batches. Serve.