- Whisk water, soy sauce, brown sugar and cornstarch together in small bowl until combined. Set aside.
- Heat oil in large wok or skillet over medium-high heat. Add beef and cook, stirring occasionally, for 4 minutes. Add carrots, bell pepper and soy sauce mixture and cook, stirring occasionally, until sauce thickens, about 2 to 3 minutes.
- Fill each lettuce leaf with steak mixture and serve with rice.
Tip: Pre-sliced peppers and matchstick carrot can usually be found in the produce aisle of your local grocer.