Preheat oven to 450°F. Slice zucchinis on an angle into 24 (½-inch-thick) slices and place in a large bowl. Add oil, rosemary, onion powder and garlic powder; toss until the zucchini is well coated. Arrange in a single layer on a large rimmed baking sheet. Roast until tender-crisp, about 5 minutes.
Meanwhile, stir mozzarella and feta together in a small bowl until combined. Remove the zucchini from the oven; flip the slices and top with the cheese mixture.
Increase oven temperature to broil. Broil the zucchini until the cheese is browned and melted, about 3 minutes. Drizzle with hot honey; garnish with rosemary, if desired. Additional reporting by Carrie Myers, M.S. and Linda Frahm
