Lightly toast pecans on a sheet in oven on 350. After removing pecans preheat oven to 425.
Pulse half the pecans, reserving remainder, in a food processor until coarsely chopped. Combine eggs and sugar and syrup until well mixed. Add butter, bourbon, vanilla, salt and orange zest.
Pour filling into prepared pie shell. Arrange reserved pecan halves on the top of filling.
At 425 degrees, bake until crust is set, about 15 min. Reduce heat to 350 and continue baking until puffed in the middle, about 1 hour.
Cool before serving - this pie is nice slightly warm or completely cooled.