Preheat the oven to 350°F (175°C).
In a large skillet over medium heat, cook the ground beef, chopped onion, and minced garlic until the beef is browned and the onion is translucent, about 7-8 minutes. Drain excess fat.
Add chili powder, ground cumin, paprika, salt, and black pepper to the beef mixture. Stir well to combine and cook for another 1-2 minutes. Remove from heat.
In a large bowl, mix together the condensed cream of mushroom soup and sour cream until smooth.
Add the cooked beef mixture to the soup mixture and stir until evenly combined.
Fold in 1/2 cup of shredded cheddar cheese and 1/2 cup of shredded Monterey Jack cheese into the beef and soup mixture.
In a greased 9×13-inch casserole dish, spread half of the crushed Doritos evenly on the bottom.
Pour the beef and cheese mixture over the Doritos layer and spread evenly.
Sprinkle the remaining crushed Doritos on top of the beef mixture.
Drizzle the melted butter evenly over the top Doritos layer.
Bake the casserole in the preheated oven for 20-25 minutes, or until the casserole is bubbly and the top is slightly golden.
Remove the casserole from the oven and sprinkle the remaining 1/2 cup cheddar cheese and 1/2 cup Monterey Jack cheese evenly over the top.
Return to the oven and bake for an additional 5 minutes, or until the cheese is melted.
Remove from oven and let the casserole rest for 5 minutes before serving.
Garnish with sliced green onions before serving.