Thoroughly scrub the lemons with warm water to remove any residue. Slice the ends off the lemon, then slice them crosswise into 1/4" thick circles.
Put the lemons in a glass bowl and add the salt, chili peppers, cinnamon stick, cloves, coriander seeds, and black peppercorns. Toss to combine, then use the palm of your hand to press down on the lemons, to extract some juice.
Pack the lemons into a glass jar and cover with the juice. If you're not using Meyer lemons, you may need to add extra lemon juice to cover the lemons.
Cover the top of the jar with plastic wrap, then use a rubber band to hold the wrap in place. Do not use a sealed lid as the lemons will release gases as they ferment
Leave the lemons in a cool dark place to ferment. You can use them after a week, but it's best to let them ferment for a couple weeks. Once they're at a place you're happy with, you can slow the fermentation by putting them in the fridge.