First step, Preheat oven to 375 degrees. In a mixing bowl, using a fork, blend together Ricotta cheese and egg. Stir in basil, thyme and garlic.
Step 2, Add 2 cups mozzarella and Parmesan cheese and toss mixture to combine. Mix in prepared spinach. Season mixture with salt and pepper to taste.
Step 03, Spread 1/3 cup marinara sauce into an even layer along bottom of a 13 by 9-inch baking dish (or similar size casserole dish). Divide cheese mixture among cooked pasta shells, stuffing each shell full with about 2 Tbsp cheese mixture.