To assemble a .zasm source file, Download the applescript below and Edit the location of the zasm executable in the property at the top of the script

Assemble zasm.scpt

Then copy to

~/Library/Application Support/BBEdit/Scripts/

and it will appear in the BBedit script menu

here is an example .zasm Z80 Assembly source file for ZX Spectrum to get you started

zasm can be found here

fuse zx spectrum emulator can be found here Fuse – the Free Unix Spectrum Emulator