In a large skillet over medium heat, add the ground beef and chopped onion. Cook until the beef is browned and the onions are translucent, about 7-10 minutes. Use a spatula to break up the meat as it cooks.
Once the beef is cooked, drain any excess fat. Stir in the green chili enchilada sauce, taco seasoning, lime juice, salt, and cayenne pepper. Let it simmer for about 5 minutes, allowing the flavors to meld.
In a separate small saucepan, heat the can of refried beans over low heat until warmed through. Stir occasionally to ensure even heating.
Spread a generous layer of refried beans on each tostada shell. Top with the seasoned beef mixture.
Add your choice of garnishes. Consider shredded lettuce for crunch, salsa for zest, avocado for creaminess, and a sprinkle of Mexican cheese for extra flavor. Drizzle with Mexican crema and finish with fresh cilantro.
Arrange your assembled tostadas on a serving platter and dig in! These are best enjoyed fresh but can also be made in advance and assembled just before serving.
