Wash the chard well. Trim the leaves away from the ribs. Cut the ribs in ¼-inch pieces and set aside, and then chop the leaves in 1-inch strips.
Heat the oil in a skillet over medium heat. Cook and stir the onion, chard ribs, garlic and chile for 5 to 10 minutes, until the onion is translucent and the chard ribs are soft. Add the chard leaves, the cilantro and the oregano and continue to cook and stir until the chard leaves have wilted and shrunk in volume. Sprinkle with the vinegar and season to taste with salt.
Pre-heat oven to 350° F. Lightly coat a 9 x 13-inch baking dish with oil and spread about ¼ cup of the enchilada sauce around the oiled dish. Set aside.
Place tortillas on a baking sheet, 4 to 6 to a pan, depending on the size of your pan. Lightly mist both sides of the tortillas with cooking spray. Heat in the oven 3 to 5 minutes, until the tortillas are soft and pliable, no more.
With your fingers, spread a heaping tablespoon of the chard filling down the middle of each tortilla. Follow with a sprinkling of the green onions and olives, and finally with about a tablespoon of the cheese. Roll the tortillas around the filling and place them seam side down in the dish. Mist, heat and fill the rest of the tortillas. (see note)
Ladle the enchilada sauce over the rolled tortillas, making a point to cover the ends first and spreading lightly over the middle. You want to be sparing vs. generous with the sauce, even if there are thumbnail patches of tortillas showing. Sprinkle with cheese, olives and green onions, for optional eye appeal.
Bake until heated through, about 20 minutes.