Preheat the oven to 350 degrees.
Grease 9 by 13 casserole dish.
In a large pot, cook the spaghetti noodles according to the al-dente directions adding the chicken bouillon to the water the pasta is being cooked in. Reserve 1.5 cups of the liquid (I have a pot with a lid that has a built-in strainer that makes this easy. Alternatively, you could use tongs to pull out the pasta from the pot and put it into a strainer, remove the liquid you need, and then dump the rest).
Return the pasta to the pot.
Add the chicken, 1 cup of the cheese, Ro-tel (and liquid), salt, cream of chicken soup, dried basil, and diced onion.
Add 1 cup of the liquid and, if the pasta still seems a bit dry…the remaining ½ cup.
Dump the pasta mixture into the greased casserole pan.
Top with the remaining cheese.
Bake for 45min - 1 hour (if the cheese starts getting to brown, cover with aluminum foil in the last 15 minutes) or until hot and bubbling.
Let cool for 15 minutes before serving.