Heat oil in a large pot over medium-high heat. Add the onion and cook until golden brown, about 5–7 minutes.
Bloom the spices:
If using, melt the butter into the onion. Once bubbly, add the crushed red pepper and garlic powder. Cook for 30 seconds.
Brown the tomato paste:
Add the tomato paste and mash it into the onion. Cook 2 minutes until it's fragrant.
Make the broth:
Pour in water and add the sugar. Bring to a boil.
Finish the broth:
Add the pasta and white beans and reduce heat to medium. Cook until al dente, about 10-15 minutes. Season with salt and pepper. Stir in the arugula and cook until wilted. Turn off the heat.
To serve:
Ladle the soup into bowls and garnish with basil, if you like. Enjoy!