I use a sealable compost bag as my shady balcony does have plenty of insects, especially gnats.
I dried my used soil, then mixed it with my kitchen scraps (after dipped in Enzyme for 2 weeks for faster composting) and pour in some water.
The usual Enzyme takes 3 months to make, but we can make a quick enzyme fertilizer in 1~2 weeks.
Prepare a plastic container (not glass as the air within the container will expand due to fermentation).
Fill 1/3 of it with fruits/vegetables waste, cut into smaller pieces to speed up the process.
Fill water up to 80% of the container. Leaving 20% empty space for gas expansion.
Expose the container to sunlight to speed up the process.
Optionally, you can add in brown sugar / molasses or EM (Effective Microorganism) or Enzyme to speed up the process.
You can harvest the liquid solution (filter away the remaining fruit waste) after 1 to 2 weeks.
Dilute it 5 to 10x before watering the plants with it (do experiment with the required dilution).
The remaining waste can be use to make compost or feed it to the worm bin.