Heat oven to 425°F.

Put the potatoes, fennel, and mushrooms directly onto a large rimmed sheet pan.

Drizzle the vegetables with about 2 tbsp olive oil. Sprinkle directly over them with about half of the oregano, paprika, garlic powder, salt, and pepper. Toss everything together right on the pan with your hands or a spatula.

Spread the vegetables into an even layer.

Pat the chicken leg quarters dry and place them skin-side up among the vegetables.

Drizzle the chicken with the remaining 1 tbsp olive oil. Season with the remaining oregano, paprika, garlic powder, salt, and pepper.

Zest about half of the lemon directly over the chicken and vegetables.

Roast for 45–55 minutes, turning the vegetables once after about 30 minutes, until the chicken is deeply browned and cooked through and the potatoes are tender.

During the last 10–15 minutes, scatter the olives over the pan.

Remove from the oven. Squeeze the lemon juice over everything while hot.

Scatter the feta over the entire pan and finish with parsley or dill, if using.

Serve straight from the sheet pan.