Heat a large skillet over medium-high heat. Add the ground beef, breaking it apart with a spatula as it cooks. Sauté until browned and no longer pink, about 6–8 minutes.

Return the skillet to medium heat and add taco seasoning along with ½ cup of water to the browned beef. Stir until well combined and let simmer for about 5 minutes.

While the beef simmers, bring a large pot of salted water to a boil. Add elbow macaroni and cook according to package instructions until al dente, usually around 7-8 minutes.

In the same pot, heat 1 tablespoon of olive oil over medium heat. Add the diced tomatoes and cook for 2–3 minutes, stirring occasionally.

Add the drained elbow macaroni and beef mixture to the pot with sautéed tomatoes. Gently stir to coat the pasta.

Lower the heat to medium and pour in 1 cup of milk, followed by the cheeses and sour cream. Stir until melted and creamy.

Remove from heat and sprinkle chopped green onions on top. Serve hot in bowls.