Prepare the lasagna noodles according to the package directions. Drain and set aside.
In a small saucepot, over medium-low heat, warm the marinara.
In a medium bowl, combine the chopped spinach, ricotta, Parmesan cheese, garlic powder, onion powder, and dried oregano or Italian seasoning. Stir to combine and warm in the microwave for about 1 minute or until the cheese softens and spinach is slightly wilted.
To Pack in a Thermos:
Preheat the thermos container with boiling water. This step is optional, but it helps.
About 5 minutes later, drain the water from the thermos.
To assemble, ladle ¼ cup marinara into a thermos, top with a lasagna noodle, then with the spinach and ricotta mixture. Top with another noodle, more sauce, Mozzarella cheese, and additional Parmesan cheese.
Close the thermos container and pack it into a lunch bag.