In large dutch oven, bring half a pot of water to boil, turn off heat and insert noodles. Allow them to soak for 15 minutes, or until about 3/4 soft, drain and rinse, set aside. Slice chicken thinly across the grain and at a slight angle, place in bowl with marinade and allow to sit while you prepare everything else. Make Pad Thai sauce, starting with dissolved Tamarind. Add fish sauce, sugar, pepper, Sriacha chili sauce, Mix well and set aside. Heat 2 tbs peanut oil in wok, add garlic and saute for 2-3 minutes. Add chicken and marinade, stir well for 3-4 minutes, Add 1/2 green onions, half the bean sprouts, and noodles. Add Pad Thai sauce, and mix gently to incorporate all together. Cook for 2-3 minutes, taste test and adjust spice or sugar as desired. Plate and garnish with remaining green onions and bean sprouts, add peanuts and cilantro. Serve immediately.