Score the fat side of the duck breast and season with salt. Pat dry with paper towels.
In a hot pan, sear the duck fat side down first for about 2 minutes.
Flip and sear for another minute.
Discard some of the duckfat in the pan and add the red curry paste. Roast for 1-2 minutes.
Add the coconut milk and bring to a simmer.
Transfer to the slow cooker.
Add in eggplants, tomatoes, pineapples, kaffir, and duck.
Cook for 5-6 hours on low.
Take the duck out and allow to roast for 15 minutes.
Carve duck and serve with curry sauce.