Line a 15 x 10 x 1-inch baking pan with several layers of paper towels.  Spread zucchini on paper towels; sprinkle with salt.  Top with another layer of paper towels.  Let stand for 15 minutes, pressing occasionally to release the excess moisture.

Remove the skin of one lemon with a zester.  Set the lemon zest aside.  A portion will be added to the fritter mix.  The rest can be saved for another use.

Meanwhile, for the lemon caper aioli, in a small bowl stir together the mayonnaise, lemon juice, capers, thyme, and black pepper.  Mix well and set aside.

Transfer zucchini to a large bowl.  Peel (if desired) and finely shred the potato.  Add the shredded potato to the zucchini along with the lemon zest, flour, baking powder, and optional cayenne pepper; toss to mix well.  Add egg; stir until combined.

In a large nonstick skillet heat 2 teaspoons olive oil over medium heat.  Working in batches, drop batter by slightly rounded tablespoons into hot skillet.  Use a spatula to flatten into patties.  Cook 4 to 5 minutes per side or until golden brown, decreasing heat, if necessary. (Keep fritters warm in 200°F oven while cooking additional batches).  Repeat with remaining batter, adding more oil as needed.  

Serve fritters immediately with the lemon caper aioli.  Makes 5 to 6 servings (3 fritters per serving).