In a small bowl, whisk together kochujang, white vinegar, and brown sugar. Add about 1 teaspoon of kosher salt and some black pepper. Note: If you think it needs more salt, taste and add another teaspoon.

In a large, heavy pot, heat olive oil on medium heat. Add the onions and cook until translucent, about 5 minutes. Add the tomatoes, crushing the tomatoes with your hands as you add them to the pot. Add the remaining tomato sauce from the can.

Add the kochujang sauce, increase heat to medium high and simmer for 10 minutes. Add the chuck roast. Bring to a low simmer, cover and slow cook until meat is very tender, stirring occasionally, about 3 hours.

Remove meat from the pot and onto a cutting board. Use a fork and knife to shred and pull apart the beef. Set aside.

Raise the heat to medium high and bring the tomato kochujang sauce to a high simmer, uncovered. Reduce the sauce until thick, about 15-20 minutes, stirring often.

Add the shredded meat back in the pot and stir until thoroughly combined and warmed through.

Serve on buns and enjoy!