In a large pot over medium heat, melt the butter. Add the garlic, dried oregano, dried basil, onion powder, and a pinch of red pepper flakes; cook 2–3 minutes until the garlic is fragrant.
Pour in 4 cups of water and increase heat to high to bring to a boil.
Add 1 teaspoon kosher salt and the penne. Cook, stirring occasionally, until the pasta is about 8 minutes into cooking (do not drain).
Stir in the whole milk, heavy cream, and room-temperature cream cheese. Cook, stirring, until the cream cheese melts and the pasta is al dente, about 4–5 more minutes.
Remove the pot from heat and stir in the grated Parmesan until the sauce is smooth and creamy. Stir in the chopped parsley and adjust seasoning with salt and black pepper to taste.
Make the arugula salad: in a small bowl whisk together the olive oil, lemon juice, finely chopped shallot, and a pinch each of red pepper flakes, salt, and pepper.
Toss the baby arugula and mixed fresh herbs with the dressing until evenly coated.
Divide the creamy penne among bowls, top with the dressed arugula and additional Parmesan if desired, and serve.