ARRANGE graham squares on bottom of 15x10x1-inch pan sprayed with cooking spray.
COOK and stir sugar, butter, water and salt in medium saucepan on medium-high heat until mixture reaches 300°F on candy thermometer (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 grahams; spread to evenly cover grahams.
SPRINKLE with nuts; cool. Melt chocolate as directed on package; drizzle over toffee. Let stand at room temperature until firm. Break into pieces.