Preheat oven to 400F and line a sheet pan with parchment paper.
Add all vegetable ingredients (potatoes, spinach, olive oil, salt, pepper, thyme) except spinach to a large mixing bowl. Combine well and spread on the prepared sheet pan.
Roast the potatoes for 15 minutes.
While potatoes bake, combine the chicken marinade ingredients in the same large mixing bowl: honey, Dijon mustard, apple cider vinegar, salt, paprika, pepper . Add the chicken thighs to the bowl, skin down.
After 15 minutes, remove the baking sheet from the oven and stir the potatoes, then move to the edges of the pan to create room for the chicken.
Rub marinade into the chicken, under the skin, then place skin side up in the middle of the baking sheet.
Return the sheet pan to the oven for 30-45 minutes (depending on your oven and the size of the thighs), until the chicken reaches 165 in the thickest part. Chicken thighs won't dry out (like chicken breasts) so there's no issue with leaving the chicken in the oven for a few extra minutes. Chicken thighs are very forgiving. I like to finish the thighs off for a few extra minutes under the broiler just to crisp up the skin.
Remove the chicken to a plate to rest.
Add the spinach to the sheet pan and stir to combine with the potatoes. Return to the oven for 5-10 minutes to wilt the spinach. If you choose to change up the leafy green and use arugula instead, don't add the arugula back to the oven.
Notes
Need more chicken?
This recipe serves one chicken thigh per person (making this meal enough for 4 people). If you want to make 6-8 total pieces of chicken, you can definitely do that. For 6, you'll have no issues. For 8, you'll need to make more sauce and also use two sheet pans: one sheet pan for the chicken and one for the veggies. The same goes for potatoes. If you want to make more potatoes, you could easily add up to 3lbs (one bag) to this recipe without issue. Add just enough oil and salt to coat. Use a second sheet pan if needed.