01 - Set oven to 350°F (180°C) to prepare for baking.
02 - Combine ricotta cheese and chopped spinach in a medium mixing bowl until evenly blended.
03 - Spread a thin layer of marinara sauce on the bottom of an 8x8-inch baking dish.
04 - Arrange three no-boil lasagna sheets over the sauce, then layer with half the ricotta-spinach mixture and half the shredded mozzarella. Repeat layering with remaining sheets, ricotta mixture, marinara, and finish with mozzarella cheese on top.
05 - Place uncovered baking dish in oven and bake for 25 minutes, or until lasagna is bubbly and golden on top.
06 - Remove from oven and let cool for 5 minutes before slicing and serving.