In a medium bowl, combine all the ingredients for the chicken marinade.
Toss in the chicken breast and marinate for at least one hour.
In a cast-iron skillet, cook chicken on high heat until there is a nice sear on the surface of the chicken, and the inside is no longer pink. Roughly six to eight minutes each side.
Set chicken aside.
Place chopped spinach, tomatoes, red onion, and avocados in a large salad bowl.
In a small bowl, combine all the ingredients for the dressing. Mix well.
Preheat the oven to gas 6, 200°C, fan 180°C.
To make the Parmesan croutons, put the chopped ciabatta cubes into a large bowl and toss with the olive oil, grated Parmesan, lemon zest and a little freshly ground black pepper.
Put on a baking sheet and put in the oven on the middle shelf to cook for 8-10 minutes, or until the croutons are nicely golden brown. Remove the tray from the oven and set aside.
Slice cooked chicken breast and add to the salad bowl.
Drizzle the salad with the dressing, lightly toss, place the salad on plates, add the chicken and serve.