Heat 1 tbsp oil in a large skillet over medium-high heat. Season chicken with salt and pepper. Cook chicken in skillet, until juices run clear, turning once, about 12 minutes. Slice into thin strips and place in a large bowl. In a small bowl, combine pepper, salt, vinegar and garlic. Slowly whisk in rest of olive oil. Add sun dried tomatoes, basil and shallot. Spoon about 1/4 cup of the dressing over the chicke, turning to coat. Toss spinach with remaining dressing and divide amoung 4 serving plates. Top with even amounts of avocado slices and chicken. Serves 4.