Whisk the Vinaigrette: In a small bowl, combine the olive oil, juice of one large lemon (about 3 tablespoons), honey, poppy seeds, and Dijon mustard. Whisk vigorously until the mixture is emulsified. Season with a small pinch of salt and pepper. Divide the vinaigrette evenly among the six small dressing containers, seal, and set aside.
Toast the Pecans: Place the pecan halves in the dry, cold cast-iron skillet over medium heat. Warm the nuts, tossing frequently, for 3–5 minutes until they are fragrant and lightly browned in spots. Immediately transfer them to a plate to cool completely, then give them a rough chop.
Season the Chicken: Pat the chicken thighs dry with a paper towel. In a separate small bowl, combine the Italian herb blend, garlic powder, ¾ teaspoon of sea salt, and ½ teaspoon of black pepper. Sprinkle the seasoning mixture evenly over all sides of the chicken.
Sear for a Golden-Brown Crust: Return the skillet to the stove over medium-high heat and add a tablespoon of olive oil to the pan. Carefully place the seasoned chicken in the hot skillet, ensuring not to overcrowd it (work in batches if necessary). Cook for 5–7 minutes per side, until a deep golden-brown crust forms and the chicken is opaque throughout.
Rest and Slice the Protein: Confirm doneness by checking that the internal temperature reaches 165°F (74°C) at the thickest point. Transfer the cooked chicken to the cutting board and let it rest for 10 minutes. This allows the juices to redistribute. Once rested, slice the chicken into thin strips.
Layer the Salad Jars: Construct your salads for optimal freshness. Start by dividing the sliced chicken among the six large jars. Follow with a layer of chopped pecans, then the quartered strawberries, and finally the crumbled goat cheese. Pack the baby spinach on top, filling the remainder of the jar.
Store for Freshness: Seal the main salad jars tightly. Refrigerate the salads and the separate dressing containers. For the best texture and flavor, enjoy within 4 days. To serve, pour the dressing into the jar, seal and shake, or empty the contents into a bowl and drizzle with the dressing.