Preheat oven to 400 degrees Fahrenheit. To shred zucchini, place a paper towel or kitchen towel under a cheese grater, grate the zucchini and squeeze out excess moisture as much as possible. Transfer to a small bowl and add minced garlic and ricotta cheese, along with a pinch of kosher salt and pepper. Stir until well combined.
Depending on the size of the chicken breasts, they may need to be pounded to about 3/4 inch thickness. To do this, place the chicken breasts on a cutting board and top with a sheet of parchment paper. Use a kitchen mallet to pound out the chicken breasts to desired thinness.
Using a sharp chefs knife, slice down the middle of the chicken breasts to the end without cutting all the way through. Mix together the garlic powder, sumac, kosher salt, and black pepper. Season both sides of the chicken breasts with the spice mixture. Spoon the ricotta filling inside the chicken breasts and place a mozzarella slice on top of the ricotta filling. Use toothpicks to secure the breasts closed on both ends.
Heat 1 tablespoon of olive oil or avocado oil in a large cast iron pan over medium high heat. Sear chicken breasts for about 3-4 minutes per side, or until just golden brown. You may need to work in batches to give the chicken enough space to brown. The toothpicks can be removed after searing on both sides.
Place all the chicken breasts in the cast iron skillet or in a large baking dish or sheet pan if making a bunch. Bake at 400 degrees for about 10-12 minutes or until chicken reaches an internal temp of 165 degrees F. Serve warm with a salad and rice, potatoes, or warm bread.
Notes
Depending on the size of the chicken breasts, this will make either 2 large or 3 smaller servings.
Use good quality ricotta - no gums, carrageenan, etc. These are brands like Calabro, Liuzzi, BelGiosio. These brands are smooth and creamy, not gritty, and it makes a difference in texture and flavor.
Mozzarella can be omitted, but it's great for extra cheesy texture.
Using a cast iron pan or one that can transfer to the oven makes for easy clean up! If cooking for a crowd, transfer the stuffed chicken breasts to a sheet pan or baking dish.