Make the brine for your tofu by whisking together ketchup, soy sauce, liquid smoke, mirin, and olive oil. Then, pour the brine into an airtight container, together with your diced tofu. Place the lid on the container and shake it up, so that your tofu is evenly coated. Place it in the fridge and let it marinate for at least one hour and up to 24 hours.
Make the gochujang sauce in advance by whisking together gochujang, soy sauce, liquid sweetener, and sesame oil. Set that aside.
Add remaining olive oil to a large cast iron skillet or regular skillet over high heat. When the oil begins to shimmer (around 1 minute), add the marinated tofu. Continue to cook, stirring occasionally, until the tofu is evenly browned (about 5 to 6 minutes). Then, add scallion whites, garlic, and kimchi, together with kimchi juice. Continue cooking until garlic is fragrant (about 3 minutes).
Before adding the rice, move the contents of the pan to the edges to create an empty space in the middle. Add a little more oil and then add your rice. Stir the rice in the center of your pan so that it becomes evenly coated with the oil. Then, add the gochujang sauce and stir until well-combined. Using the back of your spoon, gently press the rice down to create an even layer and let it cook until slightly charred on the bottom (around 3 to 5 minutes). Remove from heat and garnish with scallion greens, toasted sesame seeds, and a drizzle of toasted sesame oil. Top with optional omelet.
Notes
Please refer to Key Ingredients and Substitutions section for substitution recommendations.