Step 1Heat the oven to 400 degrees.
Step 2Season the chicken thighs all over with pepper, then arrange skin side up in a 2 ½-quart shallow baking dish wide enough for there to be a little room between each thigh. Scatter the olives around the chicken and then pour their brine over everything. Using a vegetable peeler, remove the zest from the lemon in strips and scatter them around the chicken. Chop the lemon into 1/2-inch pieces, discarding any seeds, then scatter them around the chicken as well. Drizzle everything with the olive oil.
Step 3Bake the chicken until cooked through and the skin is golden brown on top, about 1 hour.
Step 4Remove the dish from the oven and immediately transfer the chicken pieces to a plate. Stir the kale into the aromatics in the dish, then return the chicken pieces to the dish on top of the wilting greens. Use a spoon to drop chunks of avocado over the chicken and kale and season with salt, if you like.
Mozzarella: Swap 6 ounces fresh mozzarella for the avocado, breaking it into bite-size pieces to scatter over the kale.
Orange Chicken: Swap 1 orange for the lemon, omit the olives, and use ½ cup rice vinegar plus ¼ cup soy sauce instead of the brine. Swap spinach for the kale.
Spicy Greens: Add ½ to 1 teaspoon crushed red chile flakes along with the olives and swap escarole for the kale. Serve with grated parmesan.