MIx Water and Corn Starch, pour slowly into soup untill you get it as thick as you want.
You can adjust the "heat" of this by replacing the can of diced tomatoes with another Rotel to make it spicier (I do this but beware - it is very spicy), or make it milder by using mild Rotel or 2 cans of regular diced tomato. This is a very versitle recipe. Tweak it to fit your tastes.