Whisk olive oil, lemon juice, pepper sauce and thyme to blend in small saucepan over low heat. Season dressing to taste with salt and pepper. Arrange chicken and onion slices on plate. Spoon 2 tablespoons dressing over chicken and onions and turn to coat. Let chicken stand for 5 minutes. (Can be prepared up to 4 hours ahead. Cover and refrigerate.)

Prepare barbecue grill (medium-high heat). Set saucepan with remaining dressing at edge of grill to warm. Grill chicken and onion slices until just cooked through, about 5-6 minutes per side. Transfer chicken and onion to plate. Cut chicken crosswise into thin slices. Separate onion into rings.

Place lettuce in large bowl. Add chicken and onion. Add warm dressing and toss to coat. Season salad to taste with salt and pepper. Divide sald between 2 plates. Sprinkle half of feta cheese over each and serve.

Yield: 2 servings