Preheat the oven to 375° F. Mix half of the drained tomatoes and hot sauce together in a bowl, set aside.
Heat the oil in an 11 - 12-inch skillet over medium heat until shimmering. Add the onion and 1/2 teaspoon salt and cook until softened, 5 to 7 minutes. Stir in the garlic, chili powder, cumin, and oregano and cook until fragrant, about 1 minute. Stir in the beef and lightly brown, breaking up the meat with a wooden spoon, for 5 to 8 minutes.
Stir in the remaining tomatoes and reserved tomato juice. Bring to a simmer and cook until the mixture is thickened and nearly dry, about 10 minutes. Season with salt and pepper to taste.
Smooth down the ground beef with a spatula until level. Sprinkle with 1/2 cup cheese. Scatter the Fritos corn chips over the top, then sprinkle with the remaining 1/2 cup cheese.
Bake until the filling is bubbling and the top is spotty brown, about 15 minutes. Let the casserole cool for 10 minutes, then sprinkle with the green onions and lettuce, along with your choice of toppings. Serve.
Notes
Spicy heat lovers: use Original Ro-tel, otherwise I recommend Mild Ro-tel. If you can’t find Ro-tel, substitute two 1o ounce cans of diced tomatoes with chopped green chiles. Or a 14 - 15 ounce can of diced tomatoes and a 4-ounce can chopped green chiles. Save 6 tablespoons of the tomato juice and 2 tablespoons of the chile juice. You can substitute 4 ounces each of Cheddar and Monterey Jack cheeses for the Colby Jack cheese.To make Walking Taco Casserole ahead: Prepare the ground beef filling, then let cool to room temperature before continuing to assemble the casserole. Reserve corn chips, 1/2 cup cheese, and green onions. Cover with plastic wrap and refrigerate for up to 2 days. Remove the plastic wrap, top with chips, cheese, and green onions and bake as directed, increasing the cooking time to 20 minutes.