Add the pineapple chunks along with any juice to the bowl of a food processor and pulse several times until the pieces are crushed but not fully blended.
Put the crushed pineapple in a small saucepan with the sugar and lemon juice and bring to a boil. Reduce the heat to a simmer and cook for 20-25 minutes, stirring occasionally until the liquid has mostly evaporated and the jam has thickened.
Once cool, store in a tightly sealed jar in the refrigerator for up to 3 weeks or the freezer for up to 3 months.