Start by boiling your spiral pasta until it's al dente, looking tender with a slight bite. Stir it occasionally, and when it's ready, drain it well. If you do not rinse it, it can stick together, making it harder to mix later.
Whisk together the sun-dried tomato oil, white wine vinegar, minced garlic, Dijon mustard, sugar, dried herbs, salt, and pepper in a bowl. You will smell the tangy sweetness as it combines. A common mistake is to forget to taste it; adjust seasoning to get it just right.
In a large bowl, toss the cooked pasta with sun-dried tomato strips, shredded chicken, cherry tomatoes, spinach, and red onion. When everything is well mixed, you will see vibrant colors. Make sure you do not overmix; you want the veggies to stay fresh and not mushy.
Pour the dressing over the pasta mixture, gently stirring until everything is coated. It should look glossy and appealing. A tip here is to save a bit of dressing for later if you are serving it again; the salad can dry out in the fridge.
Sprinkle crumbled feta on top and give it a light toss to combine. The feta will soften a little and add creaminess. Just be careful not to crush it too much; we want those tasty bits to stand out.
Cover the salad and let it chill in the fridge for at least 30 minutes. This waiting game allows the flavors to blend beautifully. If you skip this step, the salad might taste bland because the ingredients need time to intermingle.