1bunchcilantro leaves, de-stemmed, for garnishoptional
Prepare the filling. Heat olive oil in a skillet over medium-high heat. Add onion and cook for 2 mins. Stir in green chilis and chicken, and cook for 4-5 mins, turning chicken frequently. Pour the tomatoes and 1 cup of the enchilada sauce over the chicken in the skillet and stir. Turn the heat to low-medium. Cook chicken in sauce 2-4 mins, until sauce thickens and chicken is cooked through [165 degrees].
Assemble enchiladas. First, set oven to broil. Spray a 13 x 9 baking dish with cooking spray. Spoon the remaining enchilada sauce into the pan and spread evenly. Set aside. Spoon ⅓ cup of chicken mixture onto a tortilla, and sprinkle some black olives and cheese on top. Roll tortilla and place it seam side down in casserole dish. Repeat 6-8 times until casserole dish is full. Sprinkle the casserole with more shredded cheese.
Broil enchiladas. Place casserole dish in the oven on top rack for 3-5 mins, or until cheese is golden brown and bubbly. Serve enchiladas with a dollop of sour cream and a sprig of cilantro on top.