Season steak with salt and pepper if desired. Heat oil in large deep nonstick skillet over medium-high heat and cook steak and onions, stirring occasionally, until steak is browned and onions are tender, about 5 minutes.
Stir in garlic, chili powder and ground cumin and cook, stirring, until fragrant, about 30 seconds. Add water and tomato sauce and bring to a boil over medium-high heat.
Stir in Knorr(R) Rice Sides(TM) - Beef flavor; reduce heat and simmer covered, stirring occasionally, until rice is tender, about 7 minutes. Serve, if desired, with sour cream and chopped red onion.