Line a 10" x 15" jelly roll pan with a silicon baking mat, or butter the bottom of the pan.
Spread 1 1/2 cups toasted pecans over baking sheet.
Clip a candy thermometer on large, heavy bottomed sauce pan. Over medium heat, bring butter, sugar, salt and water to a boil. Continue cooking, stirring constantly with a wooden spoon, until temperature reaches between 305 degrees F. and 315 degrees F. Keep an eye on it as it can quickly burn. Remove from heat and stir in pumpkin spice.
Carefully pour mixture over toasted nuts, spreading with a spatula to cover nuts.
Wait a few minutes then sprinkle chocolate over hot toffee, letting it melt. Use a spatula to spread chocolate over toffee.
Sprinkle 1/2 cup finely chopped and toasted nuts over warm chocolate and refrigerate until hard.
Break toffee into pieces.
Toffee does not need to be refrigerated once it has set.