Heat a 10 inch cast-iron skillet to medium heat. Add 1 Tbsp neutral oil (I used grapeseed oil). When the pan is hot, add the onion, red bell pepper, gochukaru, cumin, and salt. Saute until the vegetables are softened and slightly browned, about 5-8 minutes.
Add 1/2 cup kimchi and saute until the color is golden and orange-y, about 3-4 minutes.
Increase heat to medium high. Add ground beef and break up chunks with a wooden spoon until cooked through and brown, about 5-8 minutes. Make sure to mix the ground beef with the vegetable mixture so that it’s well combined.
Remove from oven. Add (uncooked) kimchi to the middle in a small mound. Garnish with cilantro and green onion, if desired.
Serve immediately with plenty of tortilla chips and hot sauce.
*The cheese will gradually harden as it cools. If it hardens too much, reheat in a 350F/175C oven for a few minutes until the cheese melts into runny puddles once again.
**If you don't own a cast-iron skillet, cook in a regular pot/skillet up to step 3. Transfer contents to an oven-proof bowl and mix in the cheese. Then bake for 5-10 minutes, as per usual.