1. Bring a large saucepan of water to a simmer. Add chicken and cook until no longer pink inside, 10 to 15 minutes. Transfer chicken to a plate and let cool. Using 2 forks, shred chicken; set aside 1½ cups in a large airtight container.
2. Meanwhile, in a small saucepan, cook quinoa according to package directions. Spread cooked quinoa over a baking sheet and let cool. Spoon 1 cup into the same airtight container as chicken and set aside.
3. Heat a grill pan on medium-high. Grill corn, turning often, until lightly charred, about 10 minutes. Transfer to a cutting board; let cool. Using a sharp knife, remove kernels from cobs (about 1½ cups). Discard cobs. Spoon ¾ cup kernels into same container as chicken and quinoa and set aside for Chicken Enchiladas. Refrigerate up to 2 days.
4. In a small bowl, whisk together buttermilk, 2 tbsp dill, lemon juice, mustard, salt and pepper.
5. Divide remaining quinoa among bowls. Top with coleslaw mix, tomatoes, remaining corn and chicken and avocado. Drizzle with buttermilk dressing. Top with remaining 2 tbsp dill.