Place the chicken breast in a pot, cover with water, season with a little salt and pepper, and simmer until cooked through, about 20 minutes; remove and let cool.
When cool enough to handle, shred the chicken into thin, roughly 1-inch pieces using your fingers or two forks; set aside.
Meanwhile, cut the tortillas into strips or triangles on a cutting board.
Heat a thin layer of vegetable oil in a frying pan over medium-high heat and fry the tortilla pieces until browned and crisp; transfer to a plate lined with paper towels to drain excess oil.
Heat the red sauce in a saucepan and thin with a little water if needed to reach a slightly loose consistency; season with salt and pepper to taste.
Just before removing the sauce from heat, add the shredded chicken and the fried tortilla pieces to the sauce, stirring quickly so the tortillas soak the sauce without becoming soggy.
To serve, ladle portions of sauce-soaked tortillas and chicken onto plates.
Top each portion with a drizzle of heavy cream, a sprinkle of chopped cilantro, crumbled or grated cheese, and a few thin onion rings.
