In a medium saucepot on medium heat, add the pineapple and plenty of coarse freshly cracked black pepper. Cook, stirring frequently, until the pineapple begins to bubble and brown a bit, about 20 minutes. Add the BBQ sauce, gochujang and vinegar and whisk to combine. If the mixture is too loose, cook down to a thicker consistency; if it is too thick, add a splash of water to loosen, but no more than 1/4 cup.
Let the sauce cool. When close to room temperature, stir in the cilantro.