Whisk together buttermilk, mayonnaise, vinegar, dill, mustard, green onions, salt and pepper.
Cook fusilli according to package directions, adding peas during the last 2 minutes of cooking. Drain and rinse under cold water; drain well. Toss pasta with 3/4 of the Buttermilk Dill Dressing; stir in radishes and cucumber.
Preheat grill to medium-high heat; grease grate well. Stir together olive oil, vinegar, honey, garlic, salt, thyme and paprika; toss with chicken. Marinate for 15 minutes.
Grill chicken for 5 to 7 minutes per side or until grill-marked and cooked through. Let stand for 10 minutes; slice diagonally. Toss chicken into pasta salad. Serve with remaining Buttermilk Dill Dressing.