Cook the quinoa according to package directions, then spread on a towel and let cool. Transfer the quinoa to a bowl and stir in the chia seeds and 2 tablespoons of the oil. Cover and refrigerate for 1 hour or overnight.
Add the tomato, parsley, corn and scallion and toss well. In a small bowl, mix the lemon juice, garlic, ½ teaspoon salt and ¼ teaspoon pepper; using a fork, mix in the remaining oil. Pour the dressing over the tabbouleh, toss well and season to taste.