On a lightly floured surface roll pastry into a 12-inch square; cut into a 12-inch circle. Place pastry on a 12-inch pizza pan or large baking sheet. Use a fork to generously prick pastry. Bake in a 375 degree F oven for 15 to 18 minutes or until golden (pastry will shrink). Cool.
Meanwhile, in a large mixing bowl combine the greens, artichoke hearts, and tomatoes.
For dressing, in a small bowl stir together the semisoft or cream cheese, mustard, and enough milk to make of drizzling consistency. Drizzle half of the dressing over the greens mixture, tossing to coat.
Preheat the broiler. Sprinkle 1-1/2 cups of the mozzarella cheese evenly over the crust. Broil 3 inches from the heat for 1 to 1-1/2 minutes or until the cheese melts. Spoon greens mixture evenly over melted cheese. Sprinkle with remaining mozzarella cheese. Broil 3 inches from the heat for 1 to 2 minutes more or until cheese melts. Arrange avocado slices on top. Cut into wedges. Serve at once with remaining dressing. Makes 6 servings.