Preheat oven to 375˚F.
Heat oil In a large oven-proof skillet over medium heat.
Add onion and cook for 2 minutes or until it begins to soften.
Stir in the ground beef and, using a wooden spoon, break up the meat, and cook until the beef is browned and cooked through. Drain the fat and return the pan to the burner.
Stir in 2 tablespoons flour and cook for 1 minute, then add tomato paste and stir to combine.
Add chicken broth, tomato sauce, chili powder, cumin, paprika, salt, and pepper.
Bring the mixture to a simmer. Reduce heat to low and let simmer 10 minutes.
Stir in the cooked rice, 1/2 cup cheddar, Monterey Jack cheese, and sour cream.
Top with tortilla chips and bake until the top is golden brown, about 18 to 20 minutes.
In the meantime, make the cheese sauce:
Melt the butter in a small saucepan over medium heat.
Whisk in remaining 2 tablespoons flour and cook for about a minute.
Stir in the milk and bring to a simmer.
When milk begins to thicken, stir in the remaining 2 cups of cheddar, whisking constantly until the sauce is smooth. Season with salt and pepper.
When the casserole comes out of the oven, pour the cheese sauce over the tortilla chips.
Garnish the casserole with green onions, drizzle with hot sauce, and serve.