Brick fireplace

[geome]

I want board up my chimney
I have removed the fireplace and rubble infill and have found a brick arch under the plaster.
Can I just put in a wooden frame upto the arch and cover with plasterboard or do I need a lintel as well.
Or would it be acceptable to brick it up to the arch

 

[stableroofer]

The brick arch is what they used before lintels.
Quickest way is to probably just brick it up with a few breeze blocks.
Trying to fix a timber frame inside is possible but probably more time consuming considering the arch shape at the top to get a fixing for the board.
Either way is acceptable though!