Preheat your oven to 375°F (190°C) and lightly grease a small oven-safe baking dish.
Boil the whole wheat lasagna noodles according to package instructions until al dente, then drain and set aside.
In a small skillet, sauté the diced onion and minced garlic with a tablespoon of chicken broth over medium heat until translucent.
Add the fresh spinach to the skillet and cook just until wilted, then remove from heat.
In a small bowl, whisk together the Greek yogurt, remaining chicken broth, sea salt, black pepper, and dried oregano until smooth.
Stir the cooked, shredded chicken breast into half of the yogurt sauce.
Place one lasagna noodle at the bottom of the baking dish, cutting to fit if necessary.
Layer the chicken mixture and the wilted spinach over the noodle, then top with the second noodle.
Spread the remaining yogurt sauce over the top noodle and sprinkle evenly with mozzarella and parmesan cheese.
Bake for 20 minutes until the cheese is melted and the sauce is bubbling.