How to Make It
In a medium saucepan, combine the sugar and fish sauce and cook over moderate heat, stirring, until the sugar dissolves, about 3 minutes. Remove from the heat and whisk in the lime juice. Let cool.
Meanwhile, in a small skillet, heat the canola oil. Add the peanuts and cumin and cook over moderate heat, tossing, until fragrant, about 1 minute.
Spread the lettuce in a serving bowl. In another bowl, toss the fruit and vegetables, herbs, peanuts and sesame seeds with the dressing. Pile on top of the lettuce and serve right away.
Green (unripe) papayas are very firm, with dark green skin; if unavailable, you can substitute peeled daikon or unripe mango.