Heat a heavy pan over medium-high and add the ground beef and chopped onion. Cook until the beef browns and onion softens, about 6–8 minutes.

Drain excess fat and return the pan to heat; stir in refried beans and taco seasoning until the mixture thickens and clings to the beef.

Squeeze the lime over the beef mixture and fold in chopped cilantro. Taste and adjust salt, then set the filling aside.

Spray a 13×9-inch baking dish with nonstick spray. In a large bowl, whisk the cream of chicken soup and sour cream until smooth.

Spoon a thin layer of the sour cream mixture into the bottom of the dish, then place halved tortillas flat against the edges. Cover the center with about three halves.

Spread a third of the beef mixture over the tortillas, then sprinkle with 1 cup of combined shredded cheese. Repeat layers (sour cream, tortillas, beef, cheese) and finish with a generous top layer of cheese.

If making ahead, cover and refrigerate for up to 2 days; the tortillas will soften and flavors will marry. If baking right away, preheat the oven to 350°F (175°C).

Bake uncovered for 20 minutes (30 minutes if chilled) until the top bubbles and edges turn golden. Let stand for 5–10 minutes before slicing.