Preheat oven to 350 degrees F.
Line a 10" x 15" rimmed baking with a silicon mat. Place coarsely chopped pecans on baking sheet and lightly toast pecans until barely golden brown. About 5-7 minutes. When cool, measure out 1/2 cup of the coarsely chopped pecans and chop them more finely in a food processor or by hand. These will go on top of the finished toffee. Set aside.
Leave the remaining 1 1/2 cups toasted pecans on the 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. (about 15 minutes) Keep an eye on it as it can quickly burn. It will have a golden caramel color.
Remove from heat and stir in pumpkin spice.
Carefully pour hot caramel mixture over toasted nuts, spreading with a spatula to cover nuts.
Wait a few minutes, then sprinkle chocolate chips over hot toffee, letting it melt. Use a spatula to spread chocolate over toffee.
Sprinkle the remaining 1/2 cup finely chopped and toasted nuts over warm chocolate, and refrigerate until hard.
Break toffee into pieces. Store in an airtight container.
Toffee does not need to be refrigerated once it has set.