Via the Man Upstairs:
Here are half a dozen recipes and a few observations.
I can provide Indian lime pickle recipes as well if there’s a real glut of fruit; they work perfectly for lemons, since “nimbu ka achaar” uses either or both.
However they’ll require more ingredients than preserved lemons, which at their most basic don’t need any other ingredients than Lemons, Salt and Time™ (Not Thyme!)
I’ve seen “fast preserved lemons” and “7-day preserved lemons”, but none will be as good as lemons left to mature and macerate in the salty acid for 3-4 weeks or longer.
Various preserved lemon recipes.
(1)   Plain – just lemons and salt – can be used in more ways than spiced, and not restricted to North African recipes either; the most I put in mine are a few dried Thai bird’s-eye chillies.
(2)   Try to remove all the pips when doing the initial quarter-cut; definitely remove all the pips if planning to make a purée.
(3)   Traditionally the only part used is the peel; I’m non-traditional and use the lot.
(4)   If making more than one jar, turn the contents of one into preserved-lemon purée with a processor or stick mixer. Either rinse the preserved lemon pieces and add fresh lemon juice as required, or just whizz everything. Obviously once this is done you can’t rinse off the salt and brine, so adjust the salt content of recipes where it’s used accordingly. A teaspoonful is great in sauce for fish or chicken, or mixed with mayo for sandwiches, or adding a salty tangy zing to a pot of soup, or…
Three recipes for plain salt and lemon:
https://www.daringgourmet.com/how-to-make-preserved-lemons-moroccan-middle-eastern-cooking/ This recipe adds water to top up. Don’t dilute the preservative. Use more lemon juice instead.
https://www.thekitchn.com/how-to-make-preserved-lemons-110714
https://www.simplyrecipes.com/recipes/how_to_make_preserved_lemons/
Three with spices:
https://www.thekitchn.com/recipe-preserve-5236
https://foodnetwork.co.uk/recipes/preserved-lemons/ This also suggests topping up with water. As before, use lemon juice.
https://www.bbc.co.uk/food/recipes/how_to_make_preserved_01545
Hope this helps!