Preheat oven to 350°F (175°C) to prepare for baking.
In a large skillet, brown 1 ½ pounds of ground beef with 1 cup of diced onion over medium-high heat.
Cook the ground beef until it is brown and the onions are soft, about 5-7 minutes. Drain excess grease.
Stir in the 1 tablespoon of taco seasoning and cook for another minute.
Add the 1 (10-ounce) can of Rotel, 1 (15-ounce) can of drained corn, 1 (15-ounce) can black beans, and the 1 (10-ounce) can of enchilada sauce. Stir well to combine.
Remove the skillet from the heat, and let it cool slightly. Stir in 1 cup of sour cream until it's fully combined with the meat mixture.
In a 9x13-inch casserole dish or oven-safe skillet, layer half of the Fritos on the bottom (about 1½ - 2 cups).
Spread the ground beef mixture evenly over the chips and sprinkle 1 1/2 cups of the shredded cheese on top.
Add another layer of Fritos (about 1½ - 2 cups) on top of the cheese, followed by the remaining ground beef mixture. Sprinkle the remaining 1 1/2 cups of cheese on top.
Place the casserole in the preheated oven and bake it for 15-20 minutes, or until the cheese is melted and bubbly.
Remove the walking taco bake casserole from the oven and let it rest for 2-3 minutes before garnishing.
Top the baked casserole with shredded lettuce, sliced tomatoes, sliced jalapeños, and chopped green onions or your favorite toppings. Serve your casserole immediately with extra dollop of sour cream on top or on the side if desired.