Place farro in a large saucepan; add water to cover. Bring to a boil. Reduce heat; cook, covered, until tender, 25-30 minutes.
Meanwhile, for dressing, whisk together ¼ cup oil, lime juice, garlic powder, cumin and salt. Preheat a grill pan over medium-high heat. Toss peppers with 1 teaspoon oil. Cook until all sides are blistered and blackened, 6-8 minutes, turning occasionally with tongs. Transfer to a cutting board. Chop peppers; discard stems. Transfer to a large bowl.
Brush corn with remaining 1 teaspoon oil. Cook until lightly browned and tender, 10-12 minutes, turning occasionally. Cool slightly. Cut corn from cobs; add to peppers. Drain farro; add to corn mixture. Stir in tomatoes, cheese, radishes, green onions and dressing; toss to coat. Serve warm or chilled.
