Line the insert of a 6-quart slow cooker with heavy-duty foil and spray with cooking spray.
Whisk together the maple syrup, butter, cinnamon, orange zest, salt and cayenne in a large bowl. Add the cashews and pecans and toss to coat. Add the nuts to the slow cooker in an even layer, cover and turn the heat to high. Cook until a light syrup forms at the bottom, about 1 hour.
Turn the heat to low, stir the nuts and continue to cook, stirring every 20 minutes, until the nuts are glazed and the bottom of the cooker is dry, about 1 hour.
Turn the slow cooker off, uncover and let the nuts harden, stirring occasionally, up to 2 hours. If not serving immediately, the nuts can be stored in an airtight container up to 5 days.