Mix the flour and salt in a plastic or paper bag, and shake the chicken thighs in the mixture. Set aside the chicken and dispose of the extra flour.
Heat oil in a large frying pan on high heat until it is shimmering. Add the chicken a few pieces at a time and brown nicely on all sides. Remove to a clean plate as the pieces are browned.
Once all the pieces have been browned, add the onion to the frying pan and cook over medium heat until the onion is translucent.
Add the chicken back to the pan and turn up the heat a bit.
Drizzle the chicken with the soy sauce and sprinkle on the sugar.
Stir-fry for a few minutes, until golden. Be careful: sugar burns easily!
Add the mushrooms and orange juice to the pan and simmer, covered, for about half an hour.
Add the rest of the vegetables, half a teaspoon of salt and a good grinding of pepper. Cover again and cook for about seven minutes.
If the sauce appears too runny, thicken with a mixture of 1 tbsp of cornstarch and 2 tbsp of water.
Serve with steamed rice.
