Heat a 9 or 10-inch cast-iron skillet or a large wok over medium-high heat until it's very hot, almost smoking.
Add the safflower oil, followed by the garlic, scallions, and mixed vegetables.
Stir-fry for 1-2 minutes until the vegetables begin to soften.
Add the diced tofu to the skillet and cook for 1 more minute, stirring occasionally.
Stir in the day-old rice, breaking up any clumps and spreading it evenly across the bottom of the skillet. Allow it to cook without stirring for a few minutes until the bottom layer starts to brown and get crispy.
Stir the rice and repeat the process of letting it sit to brown, continuing for about 8 minutes total, until the rice has developed plenty of crispy, crunchy bits.
Stir in the chopped kimchi, sesame oil, and sea salt.
Cook for another minute until everything is heated through.
Remove from heat, mound in bowls, and serve immediately with chili paste or tamari, if desired.
Add a Protein Boost: For ovo-vegetarians, top the finished fried rice with a sunny-side-up egg. The runny yolk creates a delicious, creamy sauce when mixed in.