Toss chicken first in 1 tablespoon dark soy sauce, then in the flour, coating pieces evenly. Heat the oil in a large skillet over medium high heat. Place chicken in the skillet, cook and stir chicken until browned, about 5 minutes. Remove chicken.
Reduce heat to medium and stir in curry paste. Cook for 1 minute until fragrant, then stir in green onions, garlic, and ginger; cook an additional 2 minutes. Return chicken to the skillet, stirring to coat with the curry mixture. Stir the coconut milk, fish sauce, 1 tablespoon soy sauce, and sugar into the chicken-curry mixture. Allow to simmer over medium heat for 20 minutes until the chicken is tender. Serve garnished with cilantro leaves.