Heat 1 tablespoon oil in large skillet over medium-high heat. Add onions and sauté until soft, about 5 minutes. Transfer onions to medium bowl.

Heat 1 tablespoon oil in same skillet. Add chicken and sauté until beginning to brown on all sides, about 5 minutes. Add buffalo sauce and bring to boil. Cover and boil until chicken is cooked through, about 15 minutes. Using slotted spoon transfer chicken to medium bowl. Cool and shred chicken. Reserve sauce in skillet.

Return chicken and onions to the reserved sauce and toss well to coat evenly. Preheat oven to low broil.

Spread tortilla chips across a large sheet pan. Evenly spread and layer the shredded chicken and cheeses on top of tortilla chips. Sprinkle olives on top of cheese.

Bake in oven for 5 minutes, until all cheese is melted. Drizzle sour cream over the nachos and top with diced tomatoes and avocado. Enjoy!