Wrap the ribeye in plastic wrap and place in the freezer for 10-15 minutes to make for easier slicing.
Combine the San-J Sweet Tamari Splash, sesame oil, gochujang, garlic, and ginger, whisking well. Reserve about one third of the mixture for serving. Pour the rest into a bowl or large food storage bag.
Using a sharp knife, slice the ribeye very thinly and add to the marinade. Marinate in the refrigerator for at least 2 hours or overnight.
Using a vegetable peeler, peel the cucumber into long ribbons. Place in a small bowl, add the rice vinegar, and let sit while making the beef.
Heat a cast iron skillet over medium-high heat. Add 1 tablespoon of oil and let it heat up. Working in batches, add steak in a single layer, being careful not to over-crowd the pan. Cook for about 1 minute per side. Set aside.
Add remaining tablespoon of oil to the pan, add the kimchi, and cook for a couple minutes just to get a little char on it.
To assemble the bowls, start with rice, then add the beef, kimchi, cucumber ribbons (drained), carrots, and microgreens. Serve with reserved sauce and lettuce leaves on the side if desired.