Toss the spinach and salad leaves together. Divide between four serving bowls and set aside.
Heat ½ tbsp of the oil in a frying pan, add the chicken and fry for 6-8 minutes until cooked through with no pink remaining. Remove with a slotted spoon, cover and keep warm. Add 1 tbsp of the oil to the pan and fry the pepper for 3-4 minutes, adding the tomatoes after 2 minutes. Remove with a slotted spoon and keep warm.
Stir the vinegar, honey and remaining oil into the pan, and simmer for 1-2 minutes until syrupy. Season with freshly ground black pepper.
Meanwhile, preheat the grill and toast the baton slices. Top with the mozzarella and grill for a further 1-2 minutes until the cheese is golden and bubbling.
Scatter the avocado, chicken, pepper and tomatoes over the salad, then top each with two cheese croûtes. Drizzle over the dressing and serve.