Rinse rice in a fine sieve colander in cold water. Rinse until water is clear.
In a 3-4 quart heavy saucepan, bring rice and 1 ¾ cups waterto a boil. Reduce heat to low. Cover and simmer for 20 minutes or until all the water is absorbed. Remove pan from heat and let sit for 10 minutes.
In a small saucepan, bring vinegar, sugar, and salt to a boil. Stir constantly until sugar is dissolved. Let cool.
Transfer the rice to a large bowl and pour vinegar mixture over rice. Fold into rice with a wooden spoon. Cover rice with a damp cloth and let cool in the refrigerator.
Whisk together wasabi paste, vegetable oil, and 1 ½tablespoons of water.
In a large bowl, toss carrots, cucumber, yellow squash, scallions, and radishes with dressing. Add rice to vegetables and toss some more. Refrigerate until ready to serve.
Before serving, slice avocado and drizzle with fresh lime juice. Garnish salad with avocado and ginger roses.