1. In a 2- to 3-quart pan over high heat, bring about 1 quart water to a boil. Add green beans and cook until tender to bite, 3 to 6 minutes. Drain and immerse immediately in ice water until cool, about 2 minutes; drain again.
2. In a blender or food processor, combine avocado, yogurt, lime juice, mint (if using), garlic, and salt; whirl until very smooth.
3. Spoon dip into a bowl and serve with green beans and jicama sticks.