Heat oven to 350'. Whisk baking powder, sugar, salt, pepper, thyme, and flour in a large bowl. Add butter and use your fingers to work into dry ingredients until largest pieces are pea sized. Drizzle in cream while running your fingers through mixture to evenly distribute; dough will begin to clump together. Add zucchini and Gruyere and gently knead until dough comes together. The less you work the dough the more tender the scones will be. Don't worry if it seems dry; zucchini will release some moisture during baking.
Turn out dough onto a lightly floured surface and pat into a 2" thick fosk. Roll out until 1" thick, then punch out scones with 3" biscuit cutter. Place on parchment lined baking sheet, about 2" apart. *Brush tops with cream and sprinkle with salt.
Bake scones, rotating halfway through, until golden brown, 30-40 minutes. Cool in wire rack.