If it is one side dish, use the first; if it is more than one side dish, use the second.
Student or Learner
There are many kinds of kimchi. So should we say:
a) Koreans eat this vegetable side dish with every meal.
b) Koreans eat these vegetable side dishes with every meal.
I'm not a Forum teacher.
I should like, If I may, Mr. naweewra, to suggest this sentence to you: Koreans usually eat a new variety of kimchi, as a side dish, with every meal.
The sentence puts emphasis on the wide variety of kimchi.
I am not a teacher.
That would make for an enormous number of different types of kimchi, don't you think? Over a thousand a year at a conservative estimate!