Pre-heat oven to 375℉
Heat a large skillet on the stovetop under medium heat. Add vegetable oil. Once vegetable oil is hot, sauté spinach until spinach is soft (shouldn't take more than a couple of minutes). Sauté in multiple batches if needed. Spinach should cook down significantly.
In a large mixing bowl, bring together cooked spinach along with all the ingredients under 'Spinach and Cheese Mixture': ricotta cheese, garlic, basil, oregano, mozzarella, parmesan, salt and black pepper. Fold to combine.
Grease a large 9'x13' casserole dish. Spoon 1/2 cup of marinara sauce and spread all over the bottom of the casserole dish.
Next, layer it with lasagna pasta, followed by half of the spinach/cheese mixture, and then 1 cup of marinara sauce.
Repeat step 5 to form another layer. When you are done, the top layer should be marinara sauce.
Sprinkle with 1 cup of mozzarella cheese, followed by 1/2 cup of parmesan cheese.
Bake in the oven for 45 minutes.
Remove from oven and let spinach lasagna cool for 10-15 minutes.
Slice lasagna. Serve and enjoy!