From Martha

This looks like a very simple meal.  If you would like a little spice in your marinade, add some finely chopped serrano peppers, and instead of scallions you might consider using chunks of the the portion of your leeks.

1 cup long-grain White Rice
1/3 cup Rice Vinegar
3 TB low Sodium Soy Sauce
4 tsp Sugar
1-inch piece fresh ginger, peeled and grated
2 tsp Vegetable Oil, plus more for brushing
1 lb Sirloin, fat trimmed, cut into 1-inch pieces
4 heads baby Bok Choy OR Tatsoi, halved
2 bunch Scallions, white and light green parts cut into 2-inch pieces

Cook rice according to package instructions.  In a medium bowl, whisk together vinegar, soy sauce, sugar and ginger until sugar is dissolved.  Reserve 2 TB marinade.  Add sirloin to the bowl, and let marinate at room temperature about 15 minutes.  Preheat broiler.  Brush a rimmed baking sheet with oil and arrange bok choy on one half of the sheet.  Whisk 2 tsps oil into reserved marinade and drizzle over bok choy.  Broil until starting to soften, about 5 minutes.  Meanwhile, thread sirloin and scallions onto 4 metal skewers.  Flip bok choy, cover with foil, and add skewers to sheet.  Broil 4 to 6 minutes more, flipping once.  Serve with rice.