Rinse the zucchini thoroughly and trim off the ends. Grate using the large side of a box grater or the grater attachment of a food processor. Combine the grated zucchini with 1 teaspoon of salt in a large bowl and let stand for 10 minutes. After resting, firmly squeeze the zucchini in handfuls over the sink to expel excess liquid—using a cheesecloth works especially well for this step. You should have about 3 1/2 to 4 cups of drained zucchini. Return the zucchini to a clean bowl and stir in the chopped green onions and beaten eggs. In a separate bowl, whisk together the all-purpose flour, baking powder, remaining 1/2 teaspoon salt, and black pepper. Add this dry mixture to the zucchini blend and mix until thoroughly incorporated. Warm a large heavy-bottomed cast iron or non-stick skillet over medium heat and pour in 2 tablespoons of olive oil. Once the oil shimmers, drop in heaping tablespoons of the batter, gently pressing each mound to form a pancake shape. Cook each fritter for 3–5 minutes on each side until golden brown, adjusting the heat as necessary to prevent over-browning. Serve immediately with a generous spoonful of sour cream.