Preheat oven to 425 degrees.
Whisk together all the ingredients for the marinade mix. Add the potatoes and onions to a baking sheet and spoon two to three table spoons of the marinade mix over them. Mix so that all the vegetables are covered. Sprinkle on half the thyme and dill. Roast for 20 minutes.
Place the chicken in a bowl and coat with the rest of the marinade. Mix with your hands to ensure the chicken is fully covered everywhere. Set it aside.
When the time is done on the potatoes, remove them from the oven and push them to one side of the pan with a spatula. Add the cut asparagus and mix together with the other vegetables.
Place the marinaded chicken thighs on the sheet pan. Discard the marinade in the bowl.
Sprinkle the breasts with the rest of the thyme and dill. Add the lemon slices to the sheet pan throughout. If you add them to the top of the chicken directly just know it can impact browning but should not impact doneness. Bake for 20-25 minutes until the chicken thighs are cooked through and the potatoes are tender.
Before serving sprinkle with a little more fresh thyme and top with sea salt and fresh cracked pepper as desired. If you want a more lemony flavor, you can squeeze a little more fresh lemon over the chicken breast too.