Bring a large pot of salted water to a boil. Add jumbo shells. 

Cook the jumbo shells until they are cooked slightly under al dente. They will cook longer in the oven. 

Strain the water from the shells and rinse the noodles with cold water and set aside. 

Preheat the oven to 400ºF and spray a 9×13-inch casserole dish with non-stick cooking spray. Set aside.

Next, heat a large skillet over medium heat and add olive oil.

When olive oil is fragrant add the shallot to the pan, sprinkle with a pinch of salt, and sauté for 1 minute. Then, add the minced garlic and saute for another minute. 

Add the fresh spinach to the pan and toss with the shallot and garlic.

Sauté the spinach over medium heat for 4-5 minutes or until the spinach is wilted and then remove from heat.

In a large bowl, mix together the ricotta cheese, ¾ cup romano, thyme, oregano, salt, pepper, and wilted spinach. Set aside.

Prepare the casserole dish and add 1 cup of your favorite marinara sauce to the bottom of the dish and spread it out with a spatula. 

Stuff the jumbo shells individually by scooping the ricotta cheese mixture with the shell until it is full. Place the shell on the bottom of the casserole, open side up. Repeat until all shells are used or until the casserole dish is full.

Finally, pour the remaining ½ cup of marinara sauce over the shells and cover the casserole dish with a top or tin foil and bake at 400ºF for 30 minutes.

Remove the casserole dish from the oven and uncover. Sprinkle mozzarella and remaining romano cheese over the shells and broil for another 2-3 minutes or until the cheese begins to brown.

Remove from the oven and top with red pepper flakes and fresh thyme.