Cook pasta as directed on package. Drain and rinse with cold water, set aside to cool.
To make the dressing, mix mayo, sugar, lime juice and poppy seeds in a bowl and whisk with a whisk. Set aside for a few minutes to allow the sugar to dissolve.
When the sugar has dissolved, pour half of the dressing over the pasta and chill for at least two hours but overnight is better to allow the pasta to absorb the flavors of the dressing.
Add the green onion, grapes, mango, avocado and chicken to your pasta. Pour on the remaining dressing. Refrigerate until ready to assemble salad then add the slivered almonds right before serving.