Combine sugar, rice vinegar, pepper, and salt in jar. Screw on the lid tightly and shake well. Let it sit for about 30 minutes at room temperature to ensure that the sugar and salt dissolve completely. Add the olive oil and shake again to mix it well.
Stir together rice, pimientos, bell pepper, scallions, corn, and beans in a medium bowl.
Toss the vinaigrette with the rice salad, then garnish and serve.