Roughly chop the kimchi. As you measure the kimchi, lightly squeeze it to extract any excess juice. Transfer the juice to a small bowl.
Add the gochujang, soy sauce, and sesame oil to the bowl with the kimchi juice. Stir everything to combine. This is your sauce.
Coat a large flat-bottomed skillet or wok with 1 tablespoon of the peanut oil and place it over medium heat.
Once the oil is hot, add the tofu cubes in a single layer. Cook the tofu for about 10 minutes, flipping the pieces about halfway through, until the pieces are golden brown and crispy.
Transfer the tofu to a plate.
Add the remaining oil to the skillet or wok and raise the heat to medium-high. Add the onion. Sauté until the onion in slightly softened, about 2 minutes.
Add the garlic and cook it with the onion for about one minute.
Add the kimchi and cook it with the onion and garlic for about 2 minutes, stirring frequently, until it begins to dry up.
Raise the heat to high and add the rice, baby bok choy, and sauce. Cook the mixture, flipping everything frequently with a spatula, until rice begins to crisp spots, about 5 to 7 minutes.
Add the tofu to the skillet or wok and flip the mixture a few times to incorporate the tofu. Take the skillet off of the burner.
Top the kimchi fried rice with scallions and sesame seeds.
Divide among plates or bowls and serve.