1.Preheat An Outdoor Grill For Medium-High Heat, And Lightly Oil The Grate. 2.Mix The Ground Beef Italian Sausage, Red Pepper Flakes, And Italian Seasoning. Form The Mixture Into 12 Thin, Wide Patties. Place About 2 Ounces Of Ricotta Cheese In The Middle Of 6 Patties. Place The Remaining 6 Patties Over The Ricotta Topped Patties, Press Down, And Pinch The Edges To Seal The Cheese In The Center. 3.Cook On The Preheated Grill Until The Burgers Are Cooked To Your Desired Degree Of Doneness, About 8 Minutes Per Side For Well Done. An Instant-Read Thermometer Inserted Into The Center Should Read 160 Degrees F (70 Degrees C). 4.Place The Cooked Burgers On Buns, Then Top With Spaghetti Sauce, Parmesan Cheese, And Spinach Leaves.