Preheat oven to 425°F (220°C). Pat the chicken thighs dry with paper towels (this helps the skin crisp). Toss halved baby potatoes in a large bowl and set aside.

In a small bowl whisk together 2 tbsp olive oil, the zest and juice of half the lemon, minced garlic, thyme, oregano, 1 tsp kosher salt and 1/2 tsp black pepper. Reserve the remaining lemon half for finishing.

Toss the potatoes with the remaining 1 tbsp olive oil, 1/2 tsp kosher salt and 1/4 tsp black pepper until evenly coated. Spread potatoes in an even layer on a rimmed baking sheet, leaving space in the center for the chicken.

Place the chicken thighs skin-side up in the center of the sheet pan. Brush or spoon the lemon-herb marinade over the skin and sides of the chicken (reserve any excess). Scatter the potatoes around the chicken in a single layer so they roast, not steam.

Roast in the preheated oven for 35-40 minutes, until potatoes are fork-tender and chicken registers 165°F (74°C) at the thickest part. Chicken skin should be deep golden and crisp; if potatoes are browning faster, move them to the outer edges of the pan.

Remove the pan, add small pats of butter over the hot chicken and potatoes, squeeze the remaining lemon half over everything, and sprinkle with chopped parsley. Let chicken rest 5 minutes before serving so juices redistribute.