In a large mixing bowl, combine Greek yogurt, minced garlic, oregano, paprika, salt, and pepper to create a flavorful marinade. Add bite-sized chicken pieces, ensuring they are thoroughly coated. Cover the bowl with plastic wrap and refrigerate for at least 30 minutes, or for enhanced flavor, marinate it overnight.

Heat a tablespoon of olive oil in a skillet over medium-high heat. Once the oil is shimmering, add the marinated chicken in a single layer, ensuring not to overcrowd the pan. Cook undisturbed for about 5 minutes, or until the chicken becomes golden brown. Flip the pieces and cook until they reach an internal temperature of 165°F, approximately another 5-7 minutes.

While the chicken marinates, make the tangy Greek yogurt dressing. In a separate bowl, whisk together Greek yogurt, olive oil, minced garlic, salt, pepper, fresh lemon juice, and dill. Adjust the dressing's consistency by adding water gradually until you reach your desired thickness. Set it aside for the flavors to meld.

In a large salad bowl, create a base with chopped romaine lettuce and fresh spinach. Once the chicken has cooled slightly, layer it over the greens. Scatter the juicy strawberries, blueberries, and crunchy pecans on top. Finish with crumbled feta cheese for a creamy touch.

Just before serving, drizzle the homemade Greek yogurt dressing over the assembled salad. Toss everything gently to ensure the delicious dressing coats each ingredient evenly.