Preheat the oven to 350°F. Wipe a baking dish with oil and set aside.
Toast the pine nuts in a dry skillet over medium high heat till they are golden and fragrant, shaking the skillet occasionally.
Heat a medium saute pan to medium high. Add 1 Tablespoon of oil, then the onions. Season with salt and pepper. Cook until softened, about 3-4 minutes. Stir in the garlic and heat 30 seconds. Add the spinach to the pan and cook until warmed through, 3-4 minutes. Stir in the lemon zest, lemon juice, feta, fresh dill, and pine nuts. Remove pan from heat and set aside to cool slightly.
Cut the chicken breasts in half horizontally. Working with one at a time, place chicken breasts between sheets of plastic wrap. Using a meat mallet, pound chicken breasts thin, ⅓-½ inch thick. Sprinkle both sides with salt and pepper.
To stuff, scoop about 3 Tablespoons of the stuffing into the center of the chicken breast. Use less if the chicken is small. Roll them up, using toothpicks to secure them closed. Place toothpick side up in the prepared baking dish. Drizzle olive oil over each chicken breast before placing the in the oven.
Bake 20-30 minutes until the juices run clear.
Mix the lemon juice and butter and pour over the chicken to serve.
Suggested accompaniments: rice, roasted potatoes, sauteed vegetables