Preheat oven to 375° and have ready a 9x13" baking dish.
On a large work surface, pat the chicken dry, drizzle with 1 tablespoon Canola oil and sprinkle with Tex-Mex seasoning. Rub all over to evenly adhere to both sides of the chicken breasts.
Add 2 tablespoons of Canola oil to a Dutch oven or large skillet over medium-high heat. Working in batches, sear the chicken for 2-3 minutes on each side, taking care not to overcrowd the pan. Transfer seared chicken to a large plate and set aside until ready to use.
Add 1 cup of ranchero sauce to the bottom of the casserole dish. Nestle the chicken into the sauce. Ladle a generous spoonful of ranchero sauce over each breast, and top with Monterey Jack cheese. Cover with foil (or place the lid on the Dutch oven) and bake for 20 minutes.
Carefully remove the aluminum foil and continue to bake for another 10 minutes. Remove from the oven and sprinkle with cilantro, if desired. Allow to cool slightly and serve alongside sliced avocados and warm flour or corn tortillas. Enjoy.