1. Heat oven to 375 degree F. Lightly grease a shallow 3-1/2- to 4-quart baking dish. For sauce, heat oil in a 12-inch skillet over medium-low heat. Add onions, bell pepper, 1/4 teaspoon of the salt and 1/4 teaspoon of the black pepper; cook 10 to 15 minutes or until vegetables soften and begin to brown. Add garlic; cook 1 minute, stirring. Add tomatoes and juice and bring to a boil; reduce heat and simmer 5 minutes more. Set aside.
2. Cut potatoes crosswise into 1/4-inch-thick slices. Thinly slice carrots on the diagonal. Cut zucchini lengthwise into 1/4-inch-thick slices. Arrange one third of the potato and carrot slices in the bottom of prepared dish. Sprinkle with 1 tablespoon of the Parmesan cheese. Arrange half of the zucchini slices over potatoes. Sprinkle with 1/8 teaspoon of the salt and 1/8 teaspoon of the black pepper. Spread one third of the sauce (1 cup) over zucchini. Sprinkle with 1/4 cup of the feta cheese. Repeat. Arrange remaining potatoes and carrots on top, spread with remaining sauce. Pour broth over vegetables, then sprinkle with remaining 2 tablespoons Parmesan.
3. Cover dish with greased foil. Bake 40 minutes. Uncover and bake 50 to 60 minutes more or until potatoes are tender and a small knife inserted in center of dish comes out easily. Let gratin stand 15 minutes before serving. Serve with tossed green salad, if desired. Makes 6 servings.