Heat a large, deep pan or wok over medium-high heat and spray with cooking spray. Season chicken breast cubes with ¾ teaspoon of the salt and the pepper before adding to the hot pan.
Cook chicken in an even layer, turning occasionally until nicely browned (5-6 minutes.) Remove browned chicken from the pan and set aside.
While chicken is cooking, rice the cauliflower using a blender or a cheese grater; set aside.
Whisk together eggs and remaining ¼ teaspoon salt in a small bowl. Spray pan with more cooking spray then reduce heat to medium.
Pour eggs into the pan and cook, stirring frequently, 1-2 minutes. Remove cooked eggs and place in the bowl with reserved chicken; set aside.
Add diced onion, scallion whites, carrots, peas, garlic, and ginger to the pan and cook until soft and tender, stirring frequently. This should take 4-5 minutes.
When veggies are cooked through, add cauliflower and soy sauce to the pan. Stir well to combine then wait for a few minutes so that the cauliflower can start to cook and create a nice crust. Come back, stir it around then wait again. The flavor comes from letting the cauliflower brown a bit and become crispy. This process may take up to 10 minutes.
Add cooked chicken and egg back to the pan and cook until warmed through. Drizzle with toasted sesame oil and garnish with scallion greens.