Preheat oven to 350°F (175°C).
In a large skillet, heat vegetable oil over medium heat.
Add diced onion and cook until softened, about 3-4 minutes.
Add minced garlic and cook for 1 minute until fragrant.
Add ground beef to the skillet and cook, breaking it apart with a spoon, until browned and cooked through, about 7-8 minutes.
Drain excess fat from the skillet.
Stir in chili powder, ground cumin, salt, and black pepper. Cook for 1 minute to combine flavors.
In a medium bowl, mix together condensed cream of mushroom soup, sour cream, milk, and half of the shredded cheddar cheese until smooth.
In a 9×13 inch casserole dish, spread half of the ground beef mixture evenly on the bottom.
Sprinkle 1 cup of Fritos corn chips evenly over the beef layer.
Pour half of the soup and sour cream mixture evenly over the Fritos layer.
Repeat the layers with remaining ground beef, remaining Fritos, and remaining soup mixture.
Sprinkle the remaining shredded cheddar cheese evenly on top.
Bake uncovered in the preheated oven for 30 minutes, until the casserole is bubbly and the cheese is melted and golden.
Remove from oven and let rest for 5 minutes before serving.