Lemon juice gives orzo and roasted carrots a bright, fresh taste.
Preheat oven to 450 degrees with a rack in lower shelf. Cut carrots diagonally into 2-inch pieces. On a rimmed baking sheet, toss carrots and garlic with 2 tablespoons oil and a pinch of salt. Roast until carrots are tender and browned, about 15 minutes. Transfer sheet to a wire rack to cool. Squeeze garlic cloves from skins; mince to form a coarse paste. Set aside.
Bring a large saucepan of water to a boil; add salt. Stir in orzo; cook until it is al dente according to package instructions, about 7 minutes. Drain; while still hot, transfer orzo to a large bowl, and toss with remaining 2 tablespoons oil. Let cool slightly, and add roasted carrots.
Meanwhile, in a small bowl, mix together lemon zest, lemon juice, scallions, and roasted garlic. Add dill, and pour mixture over orzo mixture. Stir to combine; season with salt and pepper. Serve, or store, covered with plastic wrap, in refrigerator up to 1 day; bring to room temperature before serving.