In a large bowl, mix the mango slices.
Add the sugar, lemon zest and juice, and vanilla extract. Mix well.
Transfer the mango mixture to a medium saucepan filled with water. Stir. Cover with lid. Cook. Stir occasionally. The liquid will reduce, and the jam will form. Remove the jam from the stove. Set aside to cool. Transfer to a jar.
Enjoy or refrigerate for later use!