Remove the skin from the chicken joints. Cut 3–4 slashes in the flesh of each joint, right to the bone. Mix together the turmeric, ginger, lemon juice and a little salt, then rub all over the chicken joints. Refrigerate and marinate for about 30 minutes.
Heat the oil in a large, heavy-based frying pan. Add the dried chilli and the mustard, fennel and cumin seeds, and let them splutter and pop for a few minutes. Stir in the cinnamon and besan flour. Watch carefully to be sure the spices do not burn, as this can happen very quickly.
Add the garlic, capsicum and onion to the spice mixture and cook for a few minutes, stirring. Add the chicken and tomatoes and stir to mix. Cover and cook for 15 minutes.
Meanwhile, cook the potatoes in a saucepan of boiling water for 5 minutes, then drain and cut into bite-sized pieces. Blanch the cabbage in a separate pan of boiling water for 1 minute, then drain.
Add the potatoes and cabbage to the curried chicken and stir in. Cover the pan again and continue to simmer over a moderately low heat for 20–25 minutes, or until the chicken is completely cooked and tender. Add the peas and warm through for a few minutes before serving.