When I was little my father used to make lamb kidney for breakfast on the weekends. He'd fry onions and add the chopped kidneys with lots of ground coriander, black pepper, and some cumin. Sometimes he would add mushrooms.
Lamb kidneys have such a delicate flavor. My favorite way to eat them is cut into small pieces and gently boiled/simmered in water. This works especially well if they still have their fat on them. Yum!
Make some sauce out of good lamb stock, and cream. Fry the livers, leave them pink inside.
You can dust the kidneys in colmans mustard powder, cayenne or espelette pepper etc.
Put the spices and kidneys to old paper bag and shake to distribute the spices evenly.
I dont personally salt kidneys at all since the ones i get are sufficiently salty.
I like lamb kidneys, very tender. They just go bad faster than any other offal so get them really fresh.
I can't say I really enjoy the taste of kidney but a good way to incorporate them into your diet is getting your butcher to prepare you an offal sausage. My personal recipe is 50% ground pork, 25% beef/lamb kidney, and 25% Liver (I prefer beef to lamb) and spice wise: fresh marjoram, basil and sea salt. I usually eat at least one a day... so delicious.