These are related because all of them involve frying vegetables in oil.

But they are different: 

“Poduthuval-s” [ Tamizh, Tamil ] include only those that involve just a general frying and not any boiling or additional condiments specially added.

“Thoran” [ Malayalam ] is generally chopped vegetables cooked and later fried. Coconut gratings thuvar daal etc are added in many variations.

“Mezhukkuvaratti” [ Tamizh Malayalam ] is certain vegetables mentioned, boiled and later fried without much else! These are Kerala delicasies.