First, make the coating for the chicken. In a medium bowl, whisk together sesame oil, egg whites, and 2 tbsp soy sauce. Add chicken and stir to coat, then let sit at room temperature for 20 minutes.
Steam the white rice. Bring 2 cups of water to a boil, then stir in rice, turn heat to a simmer and cover. Cook for 20 minutes. Once the rice is done, fluff with a fork and keep covered until ready for serving.
Prep the sauce. In a small bowl, stir together cornstarch, brown sugar, soy sauce, and tomato paste. Add hoisin sauce, chili oil, and rice vinegar, then whisk to combine well and set aside.
Once the chicken has rested, combine cornstarch with salt & pepper in a second bowl. Dredge chicken in the cornstarch and set aside.
In a deep cast iron frying pan, heat 2 tbsp of the vegetable oil over medium-high heat until shimmering. Add chicken in batches and fry until crispy, about 4-5 minutes, turning over once or twice as it cooks. Drain cooked chicken on paper towels and set aside. Add more oil to the pan as needed.*
Begin making the sauce. Remove the cast iron pan from heat. Add minced garlic and crushed red pepper flakes and cook until fragrant, about 10 seconds.* Add 1 cup water and scrape the bottom of the pan to stir seasonings into the water, then return pan to medium heat.
Add sauce to the frying pan. Cook until thickened, stirring constantly, about 5-6 minutes.
Add chicken to the frying pan and stir until coated in sauce. Remove from heat and serve immediately with steamed rice.*