Pound chicken breasts or thighs to 1/4 inch thin by starting in the middle and working out to the edges.
In a medium bowl, whisk the brown sugar, coconut aminos, water, grated garlic, and ginger until combined.
Place the chicken inside a glass container or large gallon zip bag and add the sauce. Seal and shake to combine.
Marinade the chicken for 30 minutes or overnight for more flavor.
In a large skillet, heat the oil over medium heat. Add the chicken and cook for 3 minutes on each side or until browned; remove from the skillet. Repeat the process with the remaining chicken, if necessary.
Once the chicken is cooked, pour the contents of the zip bag into the pan.
Bring the sauce to a boil, then reduce heat to medium-low and simmer for 2 minutes or until thickened.
Bring the chicken back to the skillet and toss to combine with the sauce. Remove from heat.
Serve over steamed rice or cauliflower rice and garnish with green onions, optional.