Preheat the oven to 425°F (220°C). Line a large rimmed sheet pan with parchment or lightly oil it so the skin doesn’t stick.
In a medium bowl whisk together the harissa paste, 3 tablespoons olive oil, honey, lemon juice, minced garlic, smoked paprika, salt and pepper until smooth. Taste and adjust salt or honey if you want it sweeter or milder.
Pat the chicken thighs dry with paper towels. Toss the thighs in the harissa mixture until well coated, then set them skin-side up on one edge of the prepared sheet pan. Let them sit at room temperature while you prep the vegetables, about 5–10 minutes (this short rest helps the marinade adhere).
In a separate bowl, toss the halved potatoes, bell pepper, red onion and cherry tomatoes with 1 tablespoon olive oil and 1/2 teaspoon kosher salt. Spread the vegetables in an even layer on the other side of the sheet pan, making sure nothing overcrowds (leave room for hot air to circulate).
Slide the pan into the center of the oven and roast for 30 minutes. Halfway through (around 15 minutes), use tongs to gently turn the potatoes and vegetables so they brown evenly and baste the chicken skins with any drippings or a little extra harissa paste if you like more color.
After 30 minutes, move the vegetables toward the center and arrange the chicken so thighs sit skin-side up with space between pieces. Roast another 8–12 minutes, until the internal temperature of the chicken reads 165°F (74°C) near the bone and the vegetables are tender and caramelized.
For extra-crispy skin, switch the oven to broil on high and broil the chicken for 2–3 minutes, watching closely so it doesn’t burn. Remove the pan and let everything rest for 5 minutes—this allows juices to redistribute and the harissa glaze to set.
Scatter chopped parsley over the chicken and vegetables and serve with lemon wedges to squeeze over top. Transfer leftovers to an airtight container once cooled and refrigerate.