You can serve this side dish hot, but it's also great at room temperature.
How to Make It
Heat a large skillet over medium heat. Add 1 tablespoon oil to pan; swirl to coat. Add onion; cook 6 minutes, stirring occasionally. Stir in tomato paste; cook 2 minutes. Stir in rind, thyme, 1/8 teaspoon salt, and pepper; cook 2 minutes, stirring occasionally.
Preheat broiler to high.
Arrange zucchini on a jelly-roll pan. Drizzle with remaining 1 tablespoon oil; toss. Broil 7 minutes or until lightly charred. Sprinkle with remaining 1/4 teaspoon salt.
Preheat oven to 375°.
Spread onion mixture in a 2-quart gratin dish. Arrange zucchini mixture over onion mixture. Sprinkle with cheese. Cover and bake at 375° for 25 minutes. Remove from oven.
Preheat broiler to high.
Uncover zucchini mixture; broil 1 1/2 minutes or until lightly browned.
Great side dish