Preheat oven to 350 degrees Fahrenheit. Spray an 8-inch round cake pan or 9-inch pie plate with non-stick cooking spray; set aside.
In a medium bowl, stir together vodka, lemon juice, cinnamon, nutmeg and sugar. Add pears and toss until fruit is completely glazed. Pour mixture into prepared pan; set aside.
In a medium microwave-safe bowl, melt the butter. Stir in flour, walnuts and sugar until well combined and crumbly. Sprinkle mixture evenly over pears.
Bake for 35-40 minutes or until topping is golden brown and bubbly. Remove from oven and let cool.
To serve, spoon pear crisp into individual serving bowls. Top with vanilla ice cream and whipped cream. Sprinkle lightly with cinnamon, if desired.