Place quinoa in a fine-mesh strainer; rinse well under cold water. Transfer to medium saucepan; add 2 cups water, 1/2 teaspoon salt. Bring to a boil over high heat. Reduce heat, cover, and simmer 15-18 minutes or until water is absorbed and quinoa is tender.
Meanwhile, cut kernels off 4 ears corn. Heat 1/4 cup olive oil over medium-high heat in a large skillet. Add corn and chopped bell peppers. Cook 10-12 minutes until tender and light brown, stirring occasionally. Add quinoa. Gently stir in tomatoes, avocado, and black beans.
Combine lime juice, sugar, cumin, and black pepper in a small bowl. Whisk in remaining 1 tablespoon olive oil until blended. Pour over quinoa mixture, toss lightly to coat. Sprinkle with cilantro. Serve warm or chilled.