In a saucepan, simmer the diced strawberries, lemon juice, sugar and vanilla for 10 mins until syrupy. Create a slurry by mixing the cornstarch and water, then stir into the saucepan. Add the halved strawberries and cook 1 min more.
Allow the strawberry topping to cool and thicken slightly. It should slowly ooze when you drizzle it with a spoon. Adjust thickness if needed by adding a touch more water or cornstarch slurry.
Remove the cheesecake from the pan and slide onto a serving plate. Spread the strawberry topping evenly over the top, arranging the halved strawberries face-down. Chill for 2 more hours.
Slice the cheesecake and serve with extra strawberry topping alongside. Leftovers keep refrigerated for 2-3 days.
