Spray a 12-cup muffin tin with vegetable cooking spray; set aside. Preheat oven to 350 degrees F.
Break spaghetti in half; cook pasta according to package directions. While pasta is cooking, mix together egg, sour cream and 1/2 cup cheese. When spaghetti is cooked al dente, drain and rinse under cold water until completely cool. Drain completely. Transfer back to cooking pot. Add sour cream mixture to the spaghetti and toss until well mixed. Set aside.
Meanwhile, cook beef in skillet until browned. Drain well and pat beef dry with paper towels. Return beef to skillet; add seasoning mix, tomato pasta and water. Mix well. Cook over medium heat 10 minutes, stirring frequently. Set aside.
Divide spaghetti mixture evenly among muffin cups (about 1/4 cup spaghetti each). Press pasta firmly into cups with back of spoon. Spoon beef mixture into center of each cup (about 1-1/2 tablespoons each), dividing evenly among cups. Top each with 1 teaspoon cheese.
Bake until firm and heated through, about 20 minutes. Let stand 8 to 10 minutes. Loosen edges with a knife and remove from muffin cups. Serve immediately.