Place crackers on greased 15 1/2 x 10 1/2 x 1-inch jelly-roll pan; set aside. In medium saucepan, over medium-high heat, heat sugar, margarine, water and salt, stirring constantly until mixture reaches 300 degrees F (hard-crack stage) or until small amount of mixture dropped into cold water separates into hard, brittle strands. Remove from heat; stir in baking soda. Immediately pour over crackers in pan, spreading evenly. Sprinkle with nuts; cool. Drizzle with melted chocolate. Let stand at room temperature to harden. Break into pieces; store in airtight container. Makes about 1 1/4 pounds.