How to repair damaged trim above window

[_Jonesy_]

The cement / mortar trim above my kitchen window has cracked and fallen down. The pieces no longer fit in the gap so I can't just wedge them back in.

In the second photo you can see the steel lintel that the brickwork sits on. There is a fairly large gap above the window now that I'm keen to get sealed.

I'm struggling to work out the best way of repairing this and haven't been quite sure what to search for. Should I fill the whole gap with mortar? Or should I use something like foam and attach trim over the top?

House is a mid 50s terrace.

Any suggestions gratefully received!

Cheers

[119]

Low expanding foam, a length of wide ish trim, tube of white silicone.