Preheat the oven to 400°F (200°C).
In a mixing bowl, combine the lemon juice, lemon zest, minced garlic, olive oil, salt, pepper, and dried thyme. Whisk until well combined.
Place the chicken breasts in the bowl with the marinade, ensuring they are evenly coated. Let them marinate for at least 10 minutes, or refrigerate for up to 1 hour for more flavor.
Prepare the asparagus by trimming the ends and placing them on a baking dish or sheet pan. Drizzle with a little olive oil and sprinkle with salt and pepper. Toss to coat.
Once marinated, remove the chicken breasts from the bowl and place them on the baking dish or sheet pan with the asparagus.
Bake in the preheated oven for 20 minutes, or until the chicken is cooked through (internal temperature should reach 165°F/75°C) and the asparagus is tender.
Remove from the oven and let the chicken rest for 5 minutes before serving.
Garnish with fresh parsley if desired and serve warm.