Place the chopped chicken, peppers, green onions, and water chestnuts in a large resealable freezer bag. Pour the bottle of kung pao sauce over everything.
Place everything from the bag into the Crock-Pot.
Dump everything from the freezer bag into a skillet.
Cook over medium-high heat until chicken is thoroughly cooked through and the sauce has thickened slightly.
If you want to make assembling this much faster, you can put the chicken breasts into the freezer bag whole and then cube them on the day of cooking either before or after cooking.