Start by patting the chicken thighs dry with paper towels to ensure crispy skin. Generously season both sides with kosher salt and ground black pepper.

In a large skillet, heat about 2 tablespoons of grapeseed oil over medium-high heat until it shimmers. Carefully place the seasoned chicken thighs skin-side down into the hot oil. Sear for 5-7 minutes until the skin turns golden brown and crispy. Flip the thighs and cook for an additional 2-3 minutes before removing them from the pan.

In the same skillet, add the whole peeled and crushed tomatoes, harissa paste, sugar, and oregano. Stir and bring the mixture to a simmer over medium heat, scraping any browned bits from the bottom of the pan for added flavor. Cook for about 8-10 minutes until the sauce thickens.

Return the seared chicken thighs to the skillet, placing them skin-side up. Lower the heat to medium-low and cover the skillet. Let the chicken simmer in the tomato sauce until it reaches an internal temperature of 165°F, about 6-8 minutes.

Remove the skillet from heat and sprinkle the chicken thighs with crumbled feta cheese and reserved oregano. Allow it to rest for a couple of minutes before serving.