Place sausage and ground beef in large saucepan over medium heat; cook and stir until meat is browned and crumbly, about 10 minutes. Add mushrooms, 1 teaspoon salt, 1/2 teaspoon black pepper, Italian herb dressing, and red pepper flakes. Turn the heat to medium-high and cook until the mushrooms have emitted their juices and the bottom of the pan is almost dry.
Pour prepared marinara sauce into meat mixture. Pour water into the marinara sauce jar and shake to get all the sauce out of the jar; add to mix. Reduce heat to low and simmer until meat is extremely tender, about 1 hour. Add a little more water if the sauce gets too thick. Skim off any excess fat from the surface of the sauce and season with more salt and black pepper, if needed. Put out the fire.
Preheat oven to 375 degrees F (190 degrees Celsius). Beat the eggs in a large bowl and add the ricotta cheese, 8 ounces diced mozzarella cheese, and 2/3 cup Parmigiano-Reggiano cheese. Season cheese mixture with 1 teaspoon salt, 1/4 teaspoon black pepper, and cayenne pepper; mix in parsley.
Bring a large pot of salted water to a boil. Cook lasagna in the boiling water, stirring occasionally, until cooked through but firm in the bite, about 8 minutes. Drain and rinse the noodles and set them aside in a bowl of cold water.
Spread 1/4 of the sauce in the bottom of a 10x15-inch baking pan. Top with 1/3 the noodles and spread 1/2 of the ricotta cheese mixture over noodles. Spread 1/4 of the meat sauce over the cheese, top with 1/3 of the noodles, and spread the remaining half of the ricotta mixture over the noodles. Spread 1/4 of the meat sauce over the cheese filling.
Lightly tap the casserole dish on a sturdy work surface to layer. Spoon the last 1/3 of the noodles over the sauce and spread 1/4 of the sauce over the noodles. Top casserole with 4 ounces cubed fresh mozzarella cheese and sprinkle with 1/2 cup Parmigiano-Reggiano.
Cover pan with foil, making sure not to touch top of pan with foil. Place the casserole on a baking sheet to catch any spills.
Bake in preheated oven for 30 minutes. Remove foil and cook until lasagna is golden brown and bubbly, 30 to 35 minutes more. Let rest for 20 minutes before cutting into squares.