In a large bowl, mix together oil, lemon zest & juice, oregano, paprika, Dijon mustard & garlic. Add chicken & potatoes to oil mixture & toss to coat.
On a large parchment lined baking sheet, arrange chicken & potatoes. Season with sea salt & pepper. Cover with foil & roast for 45 minutes.
Remove foil & toss potatoes making sure to spoon excess liquid over chicken & potatoes. Arrange lemon slices over chicken thighs & continue to cook, uncovered for another 20 minutes or until potatoes & chicken are cooked.
Remove from oven, tent with foil & let rest for 5 minutes before serving.