In a large bowl, combine olive oil, lime juice, garlic, salt, cumin, oregano, chili powder and cilantro. Add in the chicken breasts and coat evenly. Cover the bowl with plastic wrap and refrigerate for at least 20-30 minutes, or up to 3 hours.
While chicken is marinating, prepare the corn salsa. Thaw the frozen corn by placing it in a colander and rinsing with cold water until completely thawed. Drain well then add to a medium sized bowl with remaining ingredients and mix well. Refrigerate until ready to use.
Prepare quinoa according to package directions and keep warm until ready to use.
In a large skillet, heat 1 teaspoon of olive oil over medium-high heat. Add the sliced onions and frozen peppers and season to taste with salt and pepper. Cook until tender, about 5 minutes. Drain any liquid that has accumulated in the pan, then remove vegetables to a plate and set aside.
Add 1 more teaspoon of olive oil to the skillet. Remove chicken from the marinade and add to the hot skillet. Cook about 3-4 minutes per side, or until chicken is cooked through. Add the onions and peppers back into the pan and give everything a good stir.
Divide the cooked quinoa evenly between four bowls (about 3/4 cup each). Top with the fajitas, corn salsa, sliced avocado, and chopped cilantro if desired. Enjoy!