Start the grill and start cooking the rice. (I use my rice cooker and it takes 20 minutes, start to finish. You can absolutely make this with brown rice, but it takes 50 minutes to cook, so that's too long for a 31-Minute Dinner!)
Season both sides of the flank steak with salt and pepper. When the grill is hot, add steak to the grill and cook 6 to 8 minutes per side. Cooking time will depend on thickness of the filet, heat of the grill and how done you prefer your steak.
While the steak is grilling and the rice is cooking, add the tomatillos, jalapeno, cilantro leaves, salt and pepper to a small food processor and puree into fresh tomatillo salsa.
Drain the black beans and slice the cooked steak. Note: If you prefer (and have time), you can warm the beans. I just served them room temp with the warm rice.
Serve Grilled Flank Steak with Tomatillo Salsa on top with side of rice and black beans.