To make the lemon vinaigrette: Combine lemon juice, garlic, dijon mustard, honey, olive oil, salt, and pepper in a small bowl or mason jar. Mix or shake in jar until smooth.
To make the creamy feta sauce: Combine ¼ cup of the prepared lemon vinaigrette with feta cheese, greek yogurt, and chives in a food processor or blender and pulse until combined.
Add chicken into a large zip-top bag and pour ½ cup of prepared lemon vinaigrette over. Seal the bag tightly, pressing the bag gently to remove as much excess air as possible. Refrigerate and marinade for 30 minutes or up to 3 hours.
Heat an outdoor grill to medium-high heat, about 400 degrees.* Place asparagus on the grill or grill pan in an even line. Toss the asparagus periodically and cook until grill marks appear, about 6 minutes. Remove from grill and cut into 2-inch pieces.
Then, remove chicken from bag and place on grill. Grill each side for 4-6 minutes depending on thickness. Once the chicken reaches an internal temperature of 160 degrees, place chicken on a plate under foil and allow chicken to rest for 5 minutes to come up an internal temperature of 165 degrees.
If desired, grill lemon slices to serve on the side at the end.
Toss prepared romaine with asparagus and desired amount of creamy feta sauce. Top salad with chicken, cut into thin strips. Serve with grilled lemon and any extra lemon vinaigrette, as desired.
Notes
*If you don't have a grill or prefer to make the recipe inside, you can cook the chicken and asparagus in a pan over medium-high heat instead.If you end up with extra lemon vinaigrette, store in an airtight container for up to two weeks.