Whisk the gochujang, rice vinegar and soy sauce or tamari together in small bowl, set aside.
Coat a large flat-bottomed skillet with 1 tablespoon of oil and place it over medium heat. Add the tofu cubes and cook until browned on bottoms, about 5 minutes. Flip and cook about 5 minutes more. Remove from skillet and transfer to a plate.
Add the remaining oil to the skillet and raise the heat to medium-high. Add the onion and garlic. Sauté until the onion in slightly softened, about 2 minutes.
Add the kimchi and sauté 2 minutes more.
Raise the heat to high and add the rice and gochujang mixture. Cook, flipping frequently, until rice begins to crisp spots, about 5-7 minutes. Add the bok choy to the skillet. Cook about 1 minute more, flipping to incorporate the bok choy, just until wilted. Add in tofu and scallions. Flip to incorporate and remove from heat.
Add the in tofu and scallions to the skillet. Flip a few times to incorporate and remove from heat.
Divide among plates or bowls and top with sesame seeds. Serve.