Á morgnana borðar hann brauð með hunangi, en ég vil frekar sultu.

Á morgnana means in the mornings or every morning / on mornings in general.

This is different from á morgun, which means tomorrow.

So:

• á morgun = tomorrow
• á morgnana = in the mornings

That difference is very important, because they look similar but mean different things.

Because Icelandic main clauses usually follow a verb-second pattern.

That means the finite verb normally comes in the second position of the clause. If you begin with a time expression like Á morgnana, the verb comes next, and the subject follows it:

• Hann borðar brauð... = He eats bread...
• Á morgnana borðar hann brauð... = In the mornings, he eats bread...

So borðar comes before hann because Á morgnana has taken the first position.