Add grapefruit juice, oil, honey, orange zest, grapefruit zest, strawberries, and mustard to FourSide jar. Secure lid and select "Dressings." Remove vented lid insert, and add xanthan gum. Press "Pulse" 3–5 times or until dressing becomes slightly more viscous. Add poppy seeds, and press "Pulse" 2–3 times.