Cook pasta according to the direction on the package, under cooking it by about 2 minutes. Drain and set aside.
Preheat the oven to 375 F.
In a large skillet over medium-high heat, crumble in the sausage and start to brown, stirring occasionally, about 5 minutes. Add in the minced garlic and crushed red pepper and cook for another 3-4 minutes, stirring frequently.
Add in the sliced onion and let soften for about 3-4 minutes. Toss in the sliced peppers and cook for 2 minutes. Add in the tomato sauce and Italian seasoning and stir to combine. Let simmer for about 10 minutes to thicken.
Turn off the heat and add in the cooked pasta and half of the shredded cheese. Stir well to combine, then transfer to a baking dish. Sprinkle with the remaining cheese and bake at 375 F for 20-25 minutes until cheese on top is bubbling and just starting to brown.