Heat a large nonstick skillet over medium heat. Add millet; cook 10 minutes or until fragrant and toasted, stirring frequently. Add water and 1/2 teaspoon salt; bring to a boil. Cover, reduce heat, and simmer 20 minutes or until water is almost absorbed. Stir in corn kernels; cook, covered, 5 minutes. Remove millet mixture from pan, and cool to room temperature.
Combine 1/2 teaspoon salt, cilantro, and next 5 ingredients (cilantro through jalapeño). Add cilantro mixture to millet mixture, tossing to combine. Gently stir in tomato and avocado. Cover and chill 30 minutes.