Preheat the oven to 200C, fan-forced. Combine the mint and garlic seasoning and a drizzle of olive oil in a shallow dish and season with salt and pepper. Put the chicken flat on a board, put your hand on top and halve horizontally into fillets. Add the chicken to the marinade and turn to coat.
Step 2 — Cook chicken
Heat a medium frypan over medium-high heat. Cook the chicken for 2-4 mins each side until golden and cooked through. Remove from the pan and rest for 3 mins.
Step 3 — Bake garlic croutons
While the chicken is cooking, line 2 oven trays with baking paper. Coarsely tear the garlic bread into bite-sized chunks and spread, in a single layer, on a lined tray. Bake for 6-8 mins until golden and crisp.
Step 4 — Bake candied walnuts
Meanwhile, spread the walnuts, in a single layer, on the remaining lined tray. Drizzle with 2 tsp honey, season with salt and stir to coat. Bake on a separate shelf for 5-6 mins until golden.
Step 5 — Make dressing
While the croutons and walnuts are baking, put the horseradish dressing, 1 tbs extra virgin olive oil and 1 tbs white wine vinegar in a large bowl, season with salt and pepper and stir to combine.
Step 6 — Get ready to serve
Thinly slice the celery. Cut 4 'cheeks' from the apple and thinly slice, discarding the core. Add the celery, apple, spinach and garlic croutons to the dressing and toss to combine. Slice the chicken. Divide the salad and chicken among plates and drizzle the chicken with any resting juices, if desired. Scatter over the candied walnuts to serve.