Heat a large skillet over medium heat and add diced green bell pepper and red onion along with 1 teaspoon of salt. Sauté for about 10 minutes, stirring occasionally, until softened and lightly golden.

Stir in the pesto sauce and a splash of reserved pasta water into the sautéed vegetables. Simmer for about 5 minutes, stirring occasionally until it thickens slightly.

In a separate bowl, whisk all-purpose flour with a bit of warm water to create a smooth slurry. Gradually add this slurry to the pan with the heavy cream, stirring continuously.

Once thickened, add garlic powder, dried oregano, freshly chopped parsley, and black pepper to taste. Stir well and adjust seasoning as needed.

Add the cooked penne pasta directly to the sauce, gently tossing to combine. Allow everything to simmer for about 5 minutes.

Plate the creamy pesto pasta, garnishing with freshly chopped parsley and optional grated Parmesan.