Preheat oven to 400 degrees. Fill a large deep dish baking pan with half an inch of water. Lay the pepper halves in the pan and set aside.
In a large frying pan, heat oil on medium and saute onions and garlic for 5 minutes or until they start to brown. Add tomatoes and simmer for 10 minutes.
Add quinoa and chicken to the pan, Stir well and cook until bubbly.
Add 1 cup of the cheese (reserve ½ cup), cilantro, salt and pepper to taste. Mix well and remove from heat.
Stuff the pepper halves with the chicken mixture. Sprinkle with remaining ½ cup cheese.
Cover pan with foil and bake for 45 minutes or until peppers are tender. Uncover the foil for the last 5 minutes of baking.
While peppers are baking, mix together avocado, sour cream and chili powder.
Serve the cooked peppers with the avocado cream and garnish with extra cilantro if desired.