Note: If you have turnip greens available, they can be used in place of the bok choy.
Heat the butter in a large skillet over medium-high heat. Cook the onion and garlic until the onion becomes tender, approximately 3-4 minutes.
Add the bok choy and cook for 3 minutes or until it begins to brown slightly, flip and then cook an additional 3 minutes. Add the turnips (should be in approximately 1-inch pieces) and chopped tomato and cook for 1 minute.
Add the soy sauce, sesame oil and vegetable broth. Season with salt and pepper. Cover and reduce heat to medium. Cook for another 6 minutes, or until the bok choy is tender.
Transfer bok choy and turnips to a serving platter, leaving the cooking liquid in the skillet. Cook the liquid in the skillet over medium-high heat. Allow it to reduce by half, about 2 minutes.
Serve bok choy over couscous and drizzle the liquid on top.