Get ready. Set oven temperature to 350°F. Spread some baking spray or a little layer of olive oil over a 9 x 13-inch baking dish, then put it aside.
Blanch spinach and cook manicotti. Heat a big saucepan of salted water till it boils. When boiling, add the manicotti and cook, following the directions on the package, until al dente. After that, drain the manicotti and pat dry with a single paper towel layer. For approximately a minute, add the fresh baby spinach to the same boiling water to blanch it. Meanwhile, pour ice water into a small basin. Next, to prevent the spinach from cooking any further, place the blanched spinach into the ice water bath using a spider strainer or slotted spatula. After draining the cold water, carefully press out any remaining moisture by wrapping the wilted spinach in many paper towels.
Manicotti filling prepared. Toss together the spinach, ricotta cheese, shredded mozzarella cheese (reserving approximately ⅓ cup for the topping), red pepper flakes (if used), parmesan, parsley, basil, garlic paste, oregano, and salt/pepper to taste in a large mixing basin. Mixing the filling thoroughly requires stirring.
Fill manicotti clam shells. Fill a big piping bag (or use a large plastic baggie) with the filling. Taking the baking dish that has been prepared, take a ½ cup of the tomato sauce and cover the whole bottom of the pan. Subsequently, carefully push the spinach filling into the manicotti shell, taking care not to shatter the pasta shell (but it's acceptable if it does!). Next, arrange the filled manicotti shells directly over the baking pan's tomato sauce. Continue until all of the shells are constructed and filled in the dish. Over the shells, pour the leftover tomato sauce and top with the reserved shredded mozzarella.
Cook the manicotti. Put the baking dish in the oven, uncovered, and bake for 20 to 25 minutes, or until the manicotti is nicely brown and looks fantastic, and the sauce is starting to bubble.
Serve these manicotti with three cheeses and spinach right away. It tastes great on its alone, but it also tastes great when combined with garlic bread and a side salad for a full dinner. Have fun!