Preheat the oven to 220°C, fan 200°C, gas 7. Mix the yogurt and frozen garlic together and set aside. Put the baguettes on a baking tray and bake in the oven for 8-10 minutes.
Meanwhile, heat the oil in a large non-stick frying pan. Add the chicken and nearly all the spice blend (reserve a little for serving) and stir-fry over a high heat for 4-5 minutes until browned and cooked through. Remove with a slotted spoon and set aside.
Add the frozen onion and peppers to the pan and stir-fry over a high heat for 6-7 minutes until the peppers are tender and any liquid has evaporated. Return the chicken to the pan, along with half the kidney beans, and stir-fry with the peppers and onion for 1-2 minutes until piping hot.
Cut the hot baguettes in half lengthways. Pile the hot chicken and pepper mix on top of the baguette slices. Drizzle over some of the garlic yogurt and sprinkle with the remaining spice blend. Toss together the lettuce, avocado and remaining kidney beans. Serve with the remaining garlic yogurt on the side.