1. Whisk together flour, baking powder, 2 teaspoons salt, and 1/4 teaspoon pepper in a large bowl. In a separate bowl, stir together butter, eggs, and milk; add to flour mixture, and stir until just combined. Add ham (if desired), zucchini, and corn, and stir until well blended.

2. Heat 1 inch of oil in a large cast-iron skillet over medium heat until it registers 350 degrees on a deep-fry thermometer.

3. Working in batches of 4 or 5, gently drop 2 tablespoons batter into skillet for each fritter, pressing gently with a spatula to flatten. Cook, turning once, until golden brown, about 2 minutes per side. Transfer with a spatula or slotted spoon to paper towels to drain. Season fritters with salt and pepper while still hot. Make sandwiches with fritters using bacon, cheese, avocado, and tomato, if desired.