Start by cooking your rice according to package instructions.
In a large skillet over medium heat, add the ground beef and diced onion. Cook until the beef is browned and the onions are translucent, about 5-7 minutes. Drain excess fat if necessary.
Once the beef is cooked, add the soy sauce, brown sugar, pressed garlic, minced ginger, sesame oil, garlic powder, onion powder, and crushed red pepper flakes. Stir well to combine and let it simmer for 2-3 minutes.
In a small bowl, mix the corn starch and water until smooth. Pour this mixture into the skillet and stir continuously until the sauce thickens, about 1-2 minutes.
In each bowl, start with a base of rice. Top with a generous portion of the Korean beef mixture. Add the tricolor coleslaw, shredded carrots, and cucumber slices.
Finish off with a drizzle of spicy mayo and yum yum sauce if desired. Serve immediately and enjoy your delicious Korean Beef Bowls!