Preheat oven to 350°F (175°C).

In a medium saucepan, cook turnips, covered, in a small amount of boiling salted water for 4 minutes.

Add zucchini and onion to the saucepan.

Continue cooking for 3 minutes more; drain the vegetables.

In a large mixing bowl, combine the cooked turnips, zucchini, onion, chopped tomatoes, broccoli flowerets, and cauliflower flowerets.

Add 6 tablespoons of melted butter or margarine, white wine, Worcestershire sauce, garlic powder, salt, and pepper to the bowl.

Mix all ingredients thoroughly.

Turn the mixture into a 12 x 7 1/2 x 2-inch baking dish.

In a separate bowl, toss the crushed crackers with the remaining 2 tablespoons of melted butter.

Sprinkle the buttered crackers evenly over the vegetables in the baking dish.

Bake in the preheated 350°F oven for 40 minutes.

Sprinkle the shredded Cheddar cheese over the casserole.

Bake for an additional 5 minutes, or until the cheese is melted and bubbly.

Serve hot with a slotted spoon.