- 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.