Preheat oven to 425 F.
Bring a large pot of salted water to a boil. Once boiling, add pasta and cook about 5 to 6 minutes until just al dente. Drain and set aside in a large bowl.
Next, heat a large cast iron skillet over medium heat. Add sausage and cook, stirring regularly and using a wooden spoon or spatula to break up the sausage into chunks. Cook sausage until browned, about 5 minutes. Remove to a plate or small prep bowl and set aside.
To the same skillet, over medium heat, add the onion, carrot, and celery with and cook, stirring until softened, about 5 minutes. Add garlic and cook and additional 45 to 60 seconds until fragrant. Add the broccoli and peas and cook for another 5 minutes until broccoli begins to slightly soften.
Add the crushed tomatoes, dried Italian seasonings, and fresh chopped basil leaves. Give the sauce a good stir and season with a generous pinch of kosher salt and pepper. Taste to adjust seasoning as desired. Bring sauce to a simmer and add the sausage back in. Simmer sauce to allow flavors to blend together, about 5 minutes.
While the sauce simmers, prep the ricotta mixture by stirring together the ricotta, 1 cup of the mozzarella, crushed red pepper flakes, and kosher salt and pepper. Toss together with the cooked pasta. This will help the sauce stick to the cheese, which sticks to the pasta during the bake.
Add the ricotta coated pasta to the finished sauce. Gently stir to combine everything together in the cast iron skillet. Sprinkle the remaining shredded mozzarella cheese on top.
Bake for 20 to 25 minutes until golden brown and bubbly. Allow to cool for 5 to 10 minutes before serving. Garnish with a bit more chopped fresh basil leaves.