Toss the steak cubes with the Japanese BBQ sauce. Let them marinate while you prep the other ingredients to keep this recipe very low lift.
Cook the Sushi Rice
Rinse the rice until the water runs mostly clear. Cook the rice according to the instructions on the back of your bag, since different brands of sushi rice require slightly different water ratios. Once cooked, let the rice rest covered for about 10 minutes, then fluff gently.
Make the Cucumber Salad
Toss the sliced cucumbers with rice vinegar, sesame oil, and a pinch of salt. Set aside while the steak cooks.
Sear the Steak
Remove steak from marinade and lightly blot excess sauce with paper towels. Reserve the marinade.
Heat oil in a large skillet over medium-high heat. Add steak in a single layer and cook 2–3 minutes without moving to develop a crust. Flip and cook 1–2 minutes more, just until browned but not fully cooked. Transfer the steak to a plate.
Boil the Marinade
Pour the reserved marinade into the same pan. Bring to a rolling boil, then cook for 3–5 minutes until safe and slightly thickened. If it reduces too much, add a small splash of water.
Finish the Steak
Return the steak and any juices to the pan. Toss 30–60 seconds in the boiling sauce until coated and heated through. Turn off heat.
Serve
Spoon sushi rice into bowls. Top with steak bites and glossy sauce. Finish with scallions and sesame seeds. Serve the cucumber salad on the side.
Note: I made this using Bachan’s Japanese BBQ Sauce, which you can find at Whole Foods and many other grocery stores, but any brand of Japanese barbecue sauce will work.