Pat the chicken dry and sprinkle all over with enough salt and pepper to lightly coat and use your hands to press the salt/pep into the chicken so that it sticks.
In a large skillet over medium-high heat, warm the oil and swirl it to coat the skillet. Add the chicken, skin-side-down, and cook for about 5 minutes or until the skin is deeply golden and crispy. Flip and cook for 3 minutes on the other side. Transfer to a plate.
To the skillet over medium heat, add the leek and ½ teaspoon salt. Cook until the leek has softened and is beginning to brown, about 2 minutes, stirring occasionally.
Stir in the greens and cook until just wilted, about 1 minute. If using butter (see note), push the veg to the side to create space in the center and add the butter. Once melted, add the orzo, oregano, and fennel and stir to coat in the butter and then stir everything together. Let it cook to toast the orzo for about 2 minutes, stirring halfway.
Add the water and remaining ½ teaspoon salt and stir to combine. Nestle the chicken pieces back into the skillet, skin-side-up. Make sure no orzo pieces are exposed. Cover with a lid and simmer rapidly over low or medium-low heat for about 18 minutes or until the orzo is cooked through. Scatter the peas over top (if using), cover with the lid, and continue to cook for 1 more minute or until the peas are bright green/cooked/no longer frozen.
Serve it up topped with cheese, herbs, and a generous squeeze of lemon.