1In a large high-sided sauté pan with a 3-quart (2.8-L) capacity and a lid, toast the tortillas over medium-low heat one at a time until lightly browned, about 30 seconds per side. Transfer them to a plate and cut into strips about 1 inch (2.5 cm) wide; we find this easiest to do with scissors. Set the toasted tortilla strips aside.
2Add the oil to the pan and heat over medium heat. Add the onions and garlic and cook, stirring occasionally, until softened, about 6 minutes. Raise the heat to medium-high and add the beef, cumin, chili powder and cayenne. Season with salt and pepper and cook, stirring often and breaking up the meat, until the beef is browned, about 4 minutes.
3Add the tomatoes, then fill the empty can about one-third of the way with water, swish it around, and stir it into the meat sauce. Bring the mixture to a simmer, then reduce the heat to medium-low and check the seasonings (it should be a little salty). Lay half of the reserved tortilla strips evenly across the pan, pushing them under the sauce with the back of a wooden spoon. Scatter half the Cheddar cheese on top, then lay the remaining tortilla strips evenly across the pan, pushing them under the sauce again. Cover the pan and gently simmer until the sauce has thickened slightly, about 8 minutes.
4Dollop the cream cheese over the lasagna and swirl it into the sauce. Scatter the remaining Cheddar cheese on top and gently simmer, covered, until the cheese is melted, about 2 minutes. Let the lasagna rest, uncovered, for about 10 minutes, then top with the scallions, if you like, just before serving.
Tips: This recipe is a great way to use up a bag of tortillas. If you have smaller ones, a total of six should be enough; if you have larger ones, use about three.
For Staggered Serving: The lasagna is best served hot or warm. It will keep, covered, at the back of the stove for up to 2 hours. For "doctoring," you can set out some lime wedges, sour cream and hot sauce.