In saucepan, bring water, sugar, and lemon to a boil.
If using vanilla bean, scrape seeds from bean into saucepan using tip of paring knife, and then add pod.
Return to boil, stirring until sugar is dissolved.
Boil until reduced to 2 cups, 10 to 20 minutes.
Remove from heat.
Stir in Sambuca.
If using vanilla extract instead of vanilla bean, stir in extract.
Transfer syrup to bowl and let cool completely.
Stir in sliced strawberries.
Let stand at room temperature 30 minutes to 1 hour.
Discard pod before serving.