Bring a medium pot of salted water to a boil. Wash and dry produce. • Core, deseed, and dice bell pepper. Trim and thinly slice scallions, separating whites from greens.
Heat a drizzle of olive oil in a large pan over medium-high heat. Add bell pepper and cook until lightly browned and slightly softened, 3-4 minutes. • Add sausage* and scallion whites to pan; cook, breaking up meat into pieces, until browned and cooked through, 4-6 minutes. Season with salt and pepper.
Once water is boiling, add rigatoni to pot. Cook, stirring occasionally, until al dente, 9-11 minutes. • Reserve ½ cup pasta cooking water, then drain.
While pasta cooks, stir Italian Seasoning, tomato paste, and 1 tsp sugar (2 tsp for 4 servings) into pan with sausage mixture until coated. • Pour in ¼ cup plain water (1⁄3 cup for 4). Bring to a simmer and cook for 1 minute, then reduce heat to low.
Add cream sauce base to pan with sauce. Stir in 1 TBSP butter (2 TBSP for 4 servings) until melted. Season with salt and pepper.
Add drained rigatoni to pan with sauce; toss to coat. If needed, stir in reserved pasta cooking water a splash at a time until pasta is coated in a creamy sauce. • Divide pasta between bowls and top with Parmesan. Garnish with scallion greens and serve.