Method
Start the rice
Rinse the rice 3–5 times until the water is mostly clear, then drain. Transfer to a large microwave-safe bowl and add 1¼ cups water. Soak for 15–20 minutes. Cover with a microwave-safe lid that retains steam while allowing venting. Microwave for 5 minutes on HIGH, then 10 minutes at 50% power. Let rest, covered, for 10 minutes, then fluff. Microwave wattage and rice brands vary; check tenderness before serving.
Pickle the cucumber
While the rice soaks or cooks, slice the cucumber into thin rounds. Toss with rice vinegar, sesame oil, sugar or maple syrup, and salt. Let stand for 10–15 minutes, covered or refrigerated.
Mix the beef sauce
Whisk together the tamari, sesame oil, maple syrup or brown sugar, rice vinegar, garlic, ginger, and optional gochugaru.
Cook the beef
Heat the neutral oil in a large skillet over medium-high heat. Add the ground beef and cook for 5–7 minutes, breaking it apart, until browned and cooked through. Drain excess fat if needed. Reduce heat to medium. Add the sauce and simmer for 2–3 minutes, stirring to coat. Stir in most of the scallions. Keep some sauce in the pan to flavor the rice.
Assemble the bowls
Divide the warm rice between bowls. Add the beef and cucumber, then spoon over the remaining pan sauce. Finish with scallions, sesame seeds, and any optional toppings.