Preheat oven to 350 degrees F. Spray an 9x9-inch or 11x7-inch (that's what I used) baking pan with non-stick spray. Set aside.
Cook spaghetti noodles in a large pot of salted water until al dente. (According to package directions.) Drain water.
Meanwhile, cook and crumble ground beef in a large skillet over medium high heat; until beef is no longer pink. Drain any grease. Add taco seasoning and water. Cook and stir for 5 minutes.
Stir in greek yogurt, Rotel, and Velveeta cheese to hamburger mixture. Stir constantly until cheese has melted. Stir in cooked spaghetti and then pour everything into the prepared baking dish.
Top evenly with shredded cheddar cheese. Bake, uncovered, for 20 minutes or until hot and bubbly.
Serve and garnish with diced green onion. Enjoy!