Preheat oven to 425F. Line a baking sheet with parchment paper. Place zucchini in a strainer over a bowl and sprinkle with ¼ tsp salt. Toss to combine and let stand 10 minutes. Rinse and drain zucchini, then squeeze out excess liquid

In a large bowl, whisk together flour, baking powder, and remaining salt. Using a pastry blender, cut in butter until mixture resembles coarse sand, with no pieces of butter larger than the size of a pea remaining. Stir in zucchini, cheeses, sun-dried tomatoes, and basil. Add milk and stir until mixture is evenly moistened and there are no traces of dry ingredients left.

Drop ⅓-cup portions onto prepared baking sheet. Bake until golden brown, about 25 minutes. Serve warm or at room temperature. The scones can be stored in an airtight container at room temperature for up to 4 days; they can also be individually wrapped in plastic wrap, placed in a freezer Ziploc bag and frozen for up to 2 months.