Preheat the oven to 400 degrees Fahrenheit.
Cook spaghetti to al dente according to the directions on the package and then drain.
Put the ground beef into a large skillet over medium-high heat. Crumble the ground beef while it cooks. Once the ground beef is fully cooked, drain the grease from the pan.
Add water and taco seasoning to the pan and stir until all of the ground beef is coated.
Reduce the heat to low and add the spaghetti sauce and Rotel to the pan. Stir to combine.
Add cooked spaghetti noodles to the pan and stir well again.
Remove the pan from the heat and add 1 ½ cups of the shredded cheese to the pan, stir to combine.
Stand the taco shells in a 9 x 13 inch baking dish.
Scoop the spaghetti mixture into the taco shells.
Sprinkle the remaining ½ cup of cheese on top of the filled tacos.
Place the dish in the preheated oven and bake the tacos until the cheese on top is completely melted, about 4-6 minutes.
Remove the dish from the oven and serve tacos immediately.