Heat a skillet or griddle over medium heat.
Brush one side of each tortilla with oil. Lay one tortilla in the skillet, oil side down.
Sprinkle a layer of cheese over the tortilla, followed by chicken, cilantro, green onions and more cheese.
Top with tortilla, oil side up. Cook for 2-3 minutes until golden brown.
Flip carefully and cook until the other side is golden brown, about 2-3 minutes. Repeat with remaining three quesadillas.
Cut each in half and serve with sour cream.