Cabbage and red onion slaw: combine cabbage, red onion slices, green onion, sour cream, apple cider vinegar, and salt in a large bowl and stir to combine thoroughly.
Placed the slaw in a sealed container in the refrigerator for half an hour or so to cool.
Fire paste: in a medium-sized bowl, combine gochugaru, gochujang, soy sauce, vegetable oil, corn syrup (or honey), garlic, and ginger. Stir to combine. If this sauce seems like it's thicker than you'd like, you can add additional tablespoons of water or vegetable oil to get to the consistency that you might enjoy.
Store the fire paste in a sealed container in the refrigerator for up to 2 weeks.
Fried steak: pound out or butterfly the piece of steak until it's a uniform thickness of around 1/2-inch thick.
Set up the panko breadcrumb dredging station with two bowls that are big enough to hold the piece of steak. In the first bowl, crack and whisk one egg. The second bowl should contain the panko breadcrumbs, garlic powder, 1/2 teaspoon salt, and 1/2 teaspoon black pepper. Stir the panko and seasonings.
First, dip the steak in the bowl with the whisked egg. Flip the piece of meat a couple of times to ensure that it is fully coated with egg.
Next, move the egg-coated steak to the bowl with the seasoned panko breadcrumbs. Again, flip the steak several times to make sure it is fully coated with breadcrumbs.
In a medium pan over medium heat, add two tablespoons of butter and one tablespoon of olive oil.
When the butter is fully melted and bubbly, add the panko-crusted piece of steak. Cook for 4 minutes on the first side and then flip. Cook an additional 3 minutes on the second side.
After the steak has cooked on the second side, remove it to a paper towel-lined plate or a cooling rack to rest while you prepare the rest of your sandwich ingredients.
Sandwich assembly: add the fried steak on top of the bottom slice of bread.
Top the steak with 2 to 4 tablespoons of fire paste and spread it around a little. Add slaw on top of the paste and close the sandwich with the top slice of bread.
Serve and enjoy.