- Heat cranberries, sugar, vanilla, lemon juice and zest in a 3-quart saucepan over medium low heat until it simmers.
- Simmer gently, stirring occasionally, until cranberries are tender, about 15 to 20 minutes.
- Reduce heat to low and add the maple syrup and cinnamon to the pan. Simmer another few minutes.
- Remove from heat to rest for 10 minutes.
- Stir in watermelon and serve warm or chill and serve cold.