Halve the unpeeled potatoes, quartering any large ones. Put in a medium saucepan, cover with cold salted water and bring to a simmer over medium-high heat. Reduce the heat to medium and cook for 10-12 mins until tender. Drain, return to the pan and cover to keep warm.
Step 2 — Start prep
While the potato is cooking, crush or finely chop the garlic. Finely chop the thyme leaves, discarding the tough stems. Finely grate the zest of half the lemon*, then juice the half.
Step 3 — Cook chicken
Heat a chargrill pan over high heat until hot. Combine the garlic, thyme, lemon zest and 2 tsp olive oil in a large bowl and season with salt and pepper. Add the chicken and turn to coat. Reduce the heat to medium-high and cook the chicken for 5-6 mins each side until cooked through. Remove from the pan and rest for 3 mins.
Step 4 — Finish prep
Meanwhile, shred the carrot using a julienne peeler or cut into thin matchsticks. Thinly slice the celery on an angle. Coarsely shred the spinach. Coarsely chop the capers.
Step 5 — Toss salad
Put 1½ tbs extra virgin olive oil, 3 tsp lemon juice* and 1½ tsp dijon mustard in a large bowl, season with salt and pepper and whisk to combine. Add the carrot, celery and spinach and toss to combine.
Step 6 — Dress potato and serve
Combine the aioli, capers (not everyone likes capers; you can omit them here and serve separately at the table) and 2 tsp red wine vinegar in a bowl. Add the aioli dressing to the potato and gently toss to coat. Taste, then season with salt and pepper. Divide the spinach salad, potato and chicken among plates. Drizzle the chicken with any resting juices to serve.