Cut the chicken into one-inch cubes. Season with the salt, pepper, cayenne, chili powder, thyme, tarragon and chives. Mix well.
Tip: If you can plan this dish ahead, you can season the chicken and leave to marinate in the fridge overnight. You can cut them later or cut them before seasoning.
Heat the cooking oil in a wok or frying pan.
Add the chicken cubes and stir fry until no longer pink. Add the onion, ginger and garlic. Continue stir frying for another two to three minutes.
Add the tofu cubes. Season with soy sauce sauce and sugar. Stir fry until the tofu cubes are heated through.
Add the spinach. Season with fish sauce. Stir fry for another minute until the spinach is heated through.
Turn off the heat. Pour in the lemon juice. Toss a few times. Serve the chicken, tofu and spinach stir fry at once.