If students need to write about :
"What's your favourite meal ?
Is it something you eat at home or order it ? "
Should I talk about a specific food or just mention if it is lunch , dinner etc ?
Thank you

Question

If students need to write about : 
"What's your favourite meal ?
Is it something you eat at home or order it ? "
 Should I talk about a specific food or just mention if it is lunch , dinner etc ? 
Thank you

Answer

By the way, the follow-up question isn’t good English.

Is it something you eat at home or order out?
Is it something that you make at home or that you order in a restaurant?

Answer

If the question was just "What's your favorite meal?" it could be interpreted either way, but the follow-up question makes it clear that they're asking you to talk about what food or foods comprise your favorite meal.