Add the apples, strawberries, and water to a large pot and stir to combine.
Cover and cook over medium heat for 20–25 minutes, stirring occasionally, until the fruit is very soft and easily pierced with a fork.
Carefully transfer the cooked fruit and any remaining liquid to a blender, working in batches if needed.
Blend until completely smooth, then return the applesauce to the pot.
Stir in the sugar, lemon juice, and cinnamon until fully incorporated.
Taste and adjust sweetness or spice as desired, then cool before serving or storing.