In a small bowl, stir the sugar, zest of 1 lime, and cinnamon until thoroughly combined. In a 2-quart rectangular (preferably glass) baking dish, combine the rhubarb and strawberries. Sprinkle with the cinnamon-lime sugar and stir well. Let stand for 30 minutes, uncovered and at room temperature, stirring occasionally.
After 15 to 20 minutes, preheat the oven to 425°F, with a rack in the center position. Line a baking sheet with foil.
Set the baking dish on the baking sheet. Roast, uncovered, for 30 minutes, stirring once halfway through, until the juices bubble vigorously and the rhubarb is completely tender. Whisk to dissolve any chunky fruit. Cool completely. (It will thicken further as it cools.) Scrape into a lidded glass jar or other covered container and refrigerate for up to 2 weeks.
Excerpted from Yogurt Culture, © 2015 by Cheryl Sternman Rule. Reproduced by permission of Houghton Mifflin Harcourt. All rights reserved.