Finely shred potatoes and onion into a bowl of water; drain well, squeezing out excess moisture. In a large bowl combine potato mixture, eggs, flour, and salt; mix well. Press into a well-greased 15x10x1-inch baking pan. Bake in a 425 degree F. oven for 15 minutes. Brush with 1 tablespoon of the olive oil; bake 10 minutes more. Place under the broiler; broil 4 to 5 inches from the heat for 2 to 3 minutes or until golden and crisp.
Meanwhile, in a large bowl combine the zucchini, yellow squash, yellow pepper, red onion, and garlic. In a large skillet heat the remaining oil; cook the vegetable mixture, 2 cups at a time, until vegetables are crisp-tender, stirring often. Spread goat cheese over potato crust; top with cooked vegetables and tomatoes. Sprinkle with basil and mozzarella. Bake in a 425 degree F. oven for 5 to 7 minutes more or until cheese is melted. If desired, garnish with basil sprigs. Makes 8 to 10 main-dish servings.