In a 2-quart microwave-safe casserole, combine rhubarb, strawberries, and pineapple with juices. Microwave on high 7–10 minutes, stirring twice, until rhubarb is tender.
Stir in pectin. Microwave on high until mixture boils, about 2–4 minutes, stirring every minute.
Add sugar, lemon juice, and lemon zest. Microwave on high an additional 2–4 minutes, stirring every 2 minutes and letting the jam boil for about 1 minute. Let cool 10 minutes in casserole, then pour into sterilized jars. Seal, let cool, then refrigerate.