Cool cooked tri-tip in refrigerator for 2-3 hours, preferably overnight.
Preheat frying pan to medium heat.
Bring out cold tri-tip and place on cutting board. Slice thin at ¼” thickness.
Put 2 tablespoons of butter in the frying pan and coat the surface.
When butter is fully melted, add onions and pinch of salt. Stir to coat.
Once onions starts to brown, add the garlic and stir to combine.
Cook for two minutes then add the kimchi and stir.
Let the kimchi cook down for 5-7 minutes, stirring often.
Turn the heat to medium high and add in one more tablespoon of butter.
Add the tri-tip to the pan. Season with salt and pepper and stir to combine.
Once meat starts to warm, break apart with spatula (or remove to cutting board to chop, then add back to hot pan).
Once the meat is fully warmed and incorporated with the onions and kimchi, split the mixture into two piles in the pan, about the length of your bread rolls.
Place alternating pieces of provolone and havarti on top of the meat mixture.
Add water to the pan to steam and melt the cheese. Cover to melt.
Cut bread lengthwise ¾ of the way through being sure not to cut all the way through.
Remove the lid and place bread, open side down onto the meat and cheese mixtures.
Let bread steam warm on the meat for thirty seconds.
Slide spatula under the meat and flip the sandwich upright using your free hand for support.
Move to a cutting board and top with sauce and scallions.
Cut and serve hot.