What specifically makes microwavable frozen food taste so delicious?
You were advised to not cook your pasta at once, because we assumed that you are going to keep it in the fridge. With liquid water, your pasta will grow mushy or dry, depending on how wet you store it. If you freeze it, these processes will not happen, and the pasta will not degrade. 

The pasta in the supermarket frozen packages tastes good for other reasons beyond just not being mushy. It has exactly the right proportions of fat, flavoring agents and the like which will make it both cheap and tasty. Nobody can tell you the exact recipe, it is the company's secret. Their food technologists have created it after years of empirical research backed by theoretical knowledge and the availability of industrial ingredients and instruments. (If they list "modified starch", then something was done to the starch to ensure it has some characteristic; we never know what exactly was done, or what characteristic was created). 

You can try to make it for yourself, by making a sauce you like, freezing it together with the pasta and see if you like the result when defrosted. If you like it well enough, you've won. If you don't, it depends on your skill of analysing food shortcomings whether you will be able to improve it substantially. You are welcome to ask us concrete questions about concrete faults once you've done the experiment.