Make the dressing: In a small bowl or jar, whisk together the olive oil, balsamic vinegar, Dijon, honey, and garlic. Season with a pinch of salt and a few grinds of black pepper.
Taste and adjust sweetness or acidity as needed.
Prep the chicken: If using leftover or rotisserie chicken, remove the skin and shred or slice. For fresh chicken, season lightly with salt and pepper and pan-sear or grill until cooked through, then let it rest before slicing.
Toast the nuts: Warm a dry skillet over medium heat. Add almonds or pecans and toast, stirring often, for 2–3 minutes until fragrant.
Transfer to a plate to cool so they stay crisp.
Slice the produce: Hull and slice the strawberries. Thinly slice the red onion. If using avocado, slice just before serving to prevent browning.
Build the base: Add the baby spinach to a large bowl.
Drizzle with 1–2 tablespoons of the dressing and toss gently to coat the leaves. Lightly dressing the greens first helps the salad taste seasoned throughout.
Add the toppings: Layer on the chicken, strawberries, red onion, cheese, and toasted nuts. Add avocado last to keep the slices intact.
Finish and serve: Spoon over more dressing to taste.
Give everything a gentle toss, or serve as composed layers if you prefer. Taste for salt, pepper, and acidity, and adjust with a pinch of salt or a splash of balsamic if needed.