Preheat the oven to 400 degrees F (200 degrees C).
Combine dijon mustard, honey, lemon juice, thyme, salt, and pepper in a large bowl. Add chicken thighs and mix to coat with marinade.
Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add carrots, cover, and steam until carrots start to soften, 5 to 10 minutes. Use tongs to transfer carrots to a bowl and set aside. Add asparagus to steamer basket plus more boiling water if necessary. Steam asparagus until almost tender, 5 to 10 minutes, depending on the thickness of the asparagus. Add to the bowl with the carrots.
Meanwhile, heat a large oven-safe skillet over medium heat. Add olive oil and butter and let butter melt. Add marinated chicken and cook until well browned, 6 to 8 minutes. Flip chicken and cook for an additional 4 minutes. Add steamed carrots and asparagus to chicken in the skillet.
Transfer skillet to the preheated oven and roast until chicken thighs are no longer pink at the bone and the juices run clear, about 30 minutes. An instant-read thermometer inserted near the bone should read 165 degrees F (74 degrees C).