Cook spaghetti in boiling salted water according to packaging instructions.
While the spaghetti cooks, season the shrimp with cayenne pepper, Italian seasoning, salt, and pepper. Add oil to a large skillet and cook the shrimp for 1 minute on each side over medium-high heat.
Add the lemon juice to the shrimp and cook for an additional 10 seconds. Remove the shrimp from the skillet and set aside.
Add the onions to the skillet and cook for 2-3 minutes. Stir in the fresh garlic and red crushed pepper.
Add the crushed tomatoes, fresh basil, and sugar. Reduce the heat to medium-low and cook for 10 minutes.
Season the sauce with salt and pepper generously. Stir in the heavy cream and place the shrimp back into the skillet.
Add the spaghetti to the skillet and mix well.