In a medium saucepan, combine the sliced strawberries, sugar, lemon juice, and vanilla extract. Stir gently to coat the strawberries with the sugar.
In a small bowl, mix the cornstarch with the water until smooth. Add this mixture to the saucepan with the strawberries.
Cook over medium heat, stirring gently, until the mixture starts to bubble and thicken, about 5-7 minutes.
Remove from heat and let cool for about 10 minutes. The topping will continue to thicken as it cools.
Serve warm or chilled over your favorite cheesecake.