Add the orange juice, maple syrup and soy sauce to a small saucepan. Bring to a boil. Reduce heat to maintain a gentle boil, and allow to cook for 12 – 14 minutes, stirring occasionally, until sauce has thickened and coats the back of a spoon. While sauce is reducing, continue on to the next steps. (If the sauce has reached the right thickness before you are ready to add it to the chicken, turn the heat off and let sit on the stove until ready to use.)
Prep the produce and chicken: finely chop the ginger and garlic. Dice the bell pepper. Thinly slice the green onions, and separate the dark green parts from the light green/white parts. Separate the leaves of lettuce, rinse and dry them, set aside. Cut the chicken breast into small cubes, set aside.
Add the oil to a large skillet set on high heat. When oil is hot, add the bell pepper and cook for 2 minutes, stirring frequently.
Add the chicken to the bell pepper and cook for 3 minutes, stirring frequently. Chicken should be mostly opaque, but does not need to be completely cooked through at this stage.
Add the ginger, garlic, and white/light green parts of the green onion. Cook for another minute, stirring frequently.
Add the reduced sauce and cook for another minute, or until chicken is cooked through. (If sauce has not finished reducing at this stage, turn the heat off the chicken pan while the sauce finishes reducing.)
Mix the cornstarch and water together in a small bowl until no lumps remain. Pour the cornstarch slurry into the chicken. Stir and cook for 1 minute. Sauce should thicken and coat the chicken. (If it’s too thick, stir in 1 – 2 tbsp. of water or orange juice. If it’s too thin, mix an additional 1 tsp. cornstarch and 1 tbsp. water and stir in gradually, until desired texture is reached.)
Garnish with remaining green onion and serve immediately with prepared lettuce wraps.