Preheat oven to 375 degrees. In an ovenproof pot, heat butter and honey over medium heat until melted. Sprinkle tenderloin with Cajun seasoning and black pepper. Brown each side for 5 minutes in the honey butter. Lower heat if honey begins to burn.
Place pot in oven and roast uncovered for 15 - 20 minutes*.
Remove pot from oven and transfer the tenderloin to a plate. Cover with foil. Add water to the pot and stir over medium heat. Simmer for about 5 minutes, until sauce is reduced slightly. Slice on the diagonal and drizzle sauce over top to serve.
*NOTE: May need to cook longer depending on the size and thickness of the tenderloin.