Slice the sirloin steak against the grain into thin strips and chop the bell peppers into bite-sized pieces.

In a mixing bowl, combine soy sauce, brown sugar, and half of the teriyaki sauce. Add the sliced steak, ensuring it's well-coated, and let marinate for 30 minutes.

Rinse the long-grain rice under cold water until the water runs clear and cook according to package instructions.

In a skillet over medium heat, heat a drizzle of oil and sauté the chopped bell peppers for about 5 minutes.

Increase the heat slightly and add the marinated steak to the same skillet, cooking until browned on all sides, about 4 minutes.

Assemble the bowl with a base of rice, then layer with sautéed peppers and cooked steak. Drizzle with remaining teriyaki sauce, garnish with green onions and sesame seeds.