Preheat oven to 400°F. To make pork spice blend: crush coriander seeds, cumin seeds, fennel seeds, and black peppercorns with a mortar and pestle or spice grinder until somewhere between coarsely ground and a fine powder. Add garlic powder, ground thyme, paprika, and salt (about 1 tablespoon or to taste).
Heat oil in large, oven-safe skillet on stove over medium high heat. Meanwhile, rub tenderloin with dijon and coat fully with the spice blend. Once coated, sear tenderloin, browning on all sides, for five minutes total. After searing, bake in preheated oven for 20 minutes. Remove from oven, place tenderloin on cutting board and tent with foil, allowing it to rest for 10 minutes.
While tenderloin bakes and rests, heat butter or ghee over medium heat in a separate pan. Add mustard seeds and caraway seeds until you start to hear them pop. Add cabbage and onion, mixing to incorporate seeds throughout the vegetables. Cook on stove for 10 minutes, stirring occasionally. (Note: Cabbage may be practically overflowing from pan at first, but like any leafy green, will reduce considerably as it cooks).
After cooking cabbage for 10 minutes, add apple slices, garam masala, brown sugar, apple cider vinegar, and salt. Mix to incorporate, and continue to cook for an additional 20 minutes, stirring occasionally.
To serve, slice pork into medallions of desired thickness, serving on top of or alongside cabbage. Top with chopped cilantro if desired.