Preheat the oven to 350 degrees F. Spray a 9-by-13-inch baking dish with cooking spray; set aside.
Place the chicken breasts on a jelly roll pan. Drizzle each breast on both sides with 1 tablespoon olive oil. In a small bowl, mix together the taco seasoning, cumin, oregano and black pepper; sprinkle evenly over both sides of the chicken breasts. Roast for 15 to 20 minutes on each side, or until golden brown and cooked through. Remove the pan from the oven and allow to cool for 15 minutes. Shred the chicken and set aside.
Meanwhile, in a medium skillet over medium heat, melt the butter until shimmering, about 2 minutes. Add the onions and saute until soft, about 5 minutes. Add the green chiles and saute for 1 minute. Stir in the cream cheese, ranch seasoning and the shredded chicken. Cook over medium heat, stirring constantly, until the cream cheese melts, 3 to 5 minutes.
Lay the tortillas flat on a clean dry surface and spoon 2 to 3 tablespoons of the chicken mixture down the center of each. Roll up the tortillas and place them, seam-side down, in the prepared baking dish. Sprinkle with the Monterey Jack. Pour the picante sauce over the rolled tortillas and cheese. Bake until browned and bubbly, 45 minutes.