In a small bowl, combine olive oil, Dijon, lemon juice, lemon zest and thyme; season with salt and pepper, to taste. Using your fingers or a brush, work the mixture onto both sides of the chicken.
Melt butter in a large oven-proof skillet over medium high heat. Add chicken, skin-side down, and sear both sides until golden brown, about 2-3 minutes per side; set aside.
Add potatoes to the skillet; season with salt and pepper, to taste. Place into oven and bake for 18-20 minutes, or until the potatoes are easily pieced with a fork.* Add asparagus and chicken to the skillet.
Place into oven and roast until the chicken is completely cooked through, reaching an internal temperature of 175 degrees F, about 25-30 minutes.
Serve immediately.
Notes
*Cooking time will vary depending on the size and thickness of the potatoes.