In a medium bowl, whisk together warm water, warm milk, 2 tablespoons (28g) melted butter, and yeast. Let stand until foamy, 5 to 10 minutes.
In the bowl of a stand mixer fitted with the paddle attachment, beat flour, sugar, and salt at low speed until combined. Add yeast mixture and 1 egg (50g), and beat at medium-low speed for 2 minutes. Add zucchini, cheese, garlic powder, and thyme. Beat at medium-low until well combined, about 1 minute, stopping to scrape sides of bowl.
Switch to the dough hook attachment. Beat at low speed until a soft, somewhat sticky dough forms, stopping to scrape sides of bowl, 6 to 8 minutes. (Dough should pass the windowpane test; see note below.) Turn out dough onto a very lightly floured surface, and gently shape into a ball.
Spray a large bowl with cooking spray. Place dough in bowl, turning to grease top. Cover and let rise in a warm, draft-free place (75°F/24°C) until doubled in size, 30 to 45 minutes.
Prepare pan: Spray a 9-inch springform pan with cooking spray.
Divide dough into 14 portions (about 70g each). Using lightly floured hands, gently shape each portion into a smooth ball, and place in prepared pan. (Dough will fill pan.) Cover and let rise in a warm, draft-free place (75°F/24°C) until doubled in size, 30 to 45 minutes.
Preheat oven to 375°F (190°C).
In a small bowl, whisk remaining 1 egg (50g). Brush rolls with egg wash.
Bake until golden brown and an instant-read thermometer inserted incenter registers 190°F (88°C), 25 to 30 minutes, covering with foil to prevent excess browning and rotating pan halfway through baking. Immediately brush with remaining 2 tablespoons (28g) melted butter. Garnish with cheese and thyme, if desired. Serve warm. Store in an airtight container for up to 4 days.