Thinly slice chicken, and coat well with soy sauce and cornstarch or tapioca starch.
In a large nonstick frying pan or wok, heat oil over medium-high heat for 2-3 minutes until shimmering.
Add chicken and cook, stirring occasionally until lightly browned and cooked through, 4-5 minutes.
Remove chicken to a large bowl and set aside.
Add bell peppers and red onion to the pan. Cook 6-8 minutes, stirring occasionally until softened slightly. Remove to bowl with chicken.
Add snow peas, Thai chilis, ginger and cashews to the pan, and cook 2-3 minutes, stirring frequently.
Add reserved chicken and veggies back to the pan with the snow peas, chilis and ginger, and toss with sauce, reduce heat to medium and cook 4-5 minutes more, stirring occasionally, until thickened slightly.
Serve hot as is, or over prepared rice or noodles. Garnish with thinly sliced scallions and sesame seeds, if desired.