Grilled chicken salad with buttermilk dressing

Ingredients

• 1/3 cup fat-free mayonnaise
• 1/4 cup low-fat buttermilk
• 2 finely chopped tablespoons fresh dill
• 1 teaspoon minced garlic
• Cracked black pepper, to taste
• 4 boneless, skinless chicken breasts (4 ounces each)
• 2 teaspoons extra-virgin olive oil
• 8 cups torn salad greens
• 1 red bell pepper, sliced
• 1/2 sweet onion, sliced