Tools you'll need:
An Assembler (I used Z80asm with the -com option)
MCTRD (download from GitHub and build it)
Programs are broken up into a loader and the actual program.
You can create the loader in Spectaculator and save it to a .tap file.
Here's the loading code
Make a backup of the .tap file because you can use the same one for all your Spectrum projects.
Outside of Spectaculator, assemble your program (using the ORG address you specified in the loader program)
Note: if using Z80Asm, build the file as a CPM/COM file so there is no TRS-80 header on it.
Make a loading screen.
Convert it to a .scr file using SCRPlus or ZXPaintBrush
Write the loading screen (.scr) to the tape image.
./mctrd add loading game.tap
Write the game data to the tape image.
./mctrd add data game.tap
Load your tape into Spectaculator and enjoy!