Tomato and Mozzarella Tian with Ranch Bread Crumbs

Preheat oven to 400 degrees F. Heat 1 tablespoon oil in a large skillet over medium-high heat. Add onions and cook, stirring occasionally, until soft and golden, 10 to 12 minutes. Season with salt and pepper and transfer onions to a lightly oiled baking dish. Layer tomatoes and mozzarella over onions, seasoning each layer of tomatoes with salt and pepper. Drizzle with 2 tablespoons olive oil. In a small bowl, mix panko, rosemary, Hidden Valley® Original Ranch® Dips Mix, and remaining tablespoon olive oil. Sprinkle breadcrumb mixture over tomatoes and mozzarella. Bake until cheese is melted and topping is golden brown, 20 to 25 minutes. Let cool slightly before serving.