Place the chicken breasts in a mixing bowl or resealable food-storage bag and pour in the Greek vinaigrette.
Turn or massage the chicken until every surface is thoroughly covered with the dressing.
Cover the bowl or seal the bag, then refrigerate for a minimum of 2 hours. For deeper flavor, allow the chicken to marinate overnight.
Heat the grill to 350°F (175°C).
Transfer the marinated chicken breasts to the preheated grill.
Grill for 6–8 minutes per side, continuing to cook until the thickest portion of each breast reaches an internal temperature of 165°F (74°C).
Remove the cooked chicken from the grill and allow it to rest undisturbed for 10 minutes before cutting.
While the chicken cooks, prepare all of the salad components.
Add the baby spinach, diced cucumbers, Roma tomatoes, crumbled feta, chopped marinated artichoke hearts, halved Kalamata olives, mini pepperoni, sliced pepperoncini, red wine vinegar, and Greek seasoning to a large mixing bowl.
Gently toss the mixture until the vegetables, cheese, and seasonings are evenly dispersed.
After the grilled chicken has rested, cut it into bite-sized cubes and transfer the pieces to the prepared salad.
Drizzle the additional Greek vinaigrette over the mixture, then toss gently until the chicken and salad ingredients are evenly coated.
Divide the cottage cheese among serving plates or bowls, creating a generous base for each portion.
Spoon the Greek chicken and salad mixture over the cottage cheese and serve immediately.