Position rack in top third of oven and preheat to 400°F. Combine 3 eggs, half of onions, and half of green onions in processor. Blend until mixture is almost smooth and fluffy. Add half of potatoes, half of carrots, and half of zucchini. Blend until vegetables are finely chopped (bits of carrots and zucchini will remain). Transfer mixture to large bowl. Repeat with remaining 2 eggs, onions, and green onions, then potatoes, carrots, and zucchini. Add to mixture in bowl. Whisk in matzo meal, 2 1/2 teaspoons salt, and 1/2 teaspoon pepper, then 1/4 cup margarine. Brush remaining 1/4 cup margarine over bottom and sides of 13x9x2-inch glass baking dish. Place dish in oven until very hot, about 7 minutes. Pour kugel batter into hot dish. Bake until top is brown and crisp, about 1 hour. Cut kugel into squares; serve hot alongside brisket.