Cut the pork tenderloin into small 1/2-inch cubes to mimic the texture of traditional pork belly while keeping it lean.
In a small glass bowl, whisk together the gochujang, tamari, toasted sesame oil, minced ginger, and minced garlic until smooth.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Add the pork cubes in a single layer and sear for 3-4 minutes without moving them to develop a golden-brown, crispy crust.
Pour the gochujang sauce mixture over the pork and toss continuously for 2 minutes until the sauce reduces into a thick, sticky glaze.
Transfer the pork to a plate and add the chopped bok choy to the same skillet, sautéing for 90 seconds in the residual glaze until bright green.
Build your bowl by layering the warm brown rice at the bottom and topping it with the glazed pork, sautéed bok choy, and chilled kimchi.
Finish the dish with a sprinkle of sesame seeds and thinly sliced green onions for a fresh, sharp bite.