1. Put the coriander, lime juice, broth, spring onions, garlic, jalapeno, honey, and salt in a blender, puree until smooth. Reserve 2 tablespoons; do not wash out the blender.
2. Put chicken breasts in a medium bowl and the peppers and onions in another. Divide the remaining coriander puree evenly between the chicken and the peppers and onions. Toss well to coat the chicken and vegetables and let stand, at room temperature, for up to 30 minutes.
3. Add the avocado, 120ml water, and the reserved 2 tablespoons coriander sauce to the blender. Puree until smooth and season with salt. Set aside.
4. Heat the oil in a small frying pan set over medium heat until hot. Add the cumin and coriander and continue to cook until fragrant, about 30 seconds to 1 minute. Pour the spices over the yogurt and set aside for the flavors to blend. Stir before serving.
5. Preheat a grill for medium-high/direct heat cooking. Oil the grill grates. Grill the chicken and vegetables, turning, until the vegetables are tender and the chicken reaches an internal temperature of 71°C, about 5 to 8 minutes for the vegetables and 12 to 15 minutes for the chicken. Let chicken rest 5 minutes. Place the tortillas on the grill until just warmed through, about 30 seconds.
6. To assemble the fajitas: slice the onions and peppers into thin strips and then slice the chicken. Place some peppers, onions, chicken and coriander in a tortilla topped with the spiced yogurt and the avocado sauce.