Heat the olive oil in a large pot or Dutch oven over medium heat. Add the sliced garlic and red pepper flakes, if using. Cook for about 30 seconds until fragrant, stirring so the garlic doesn't brown.
Pour in the diced tomatoes and 1 cup (240 ml) of water. Season with salt. Bring to a simmer, then cover, reduce the heat to low, and let it cook for 5 minutes.
Add the cannellini beans with all their liquid from the can, along with the chopped parsley. Stir well and bring the mixture back to a gentle simmer.
Stir in the uncooked pasta. Cook, stirring frequently to prevent sticking, for about 10 minutes.
As the pasta cooks and absorbs the liquid, gradually add the remaining 1 cup (240 ml) of water. Continue stirring often.
The dish is done when the pasta is cooked al dente and the sauce has thickened into a creamy consistency that coats the pasta and beans.
Remove the pot from the heat. Stir in the grated Parmesan cheese and black pepper. Taste and add more salt if needed.
Serve immediately in bowls, garnished with extra parsley, a sprinkle of Parmesan, and a drizzle of good olive oil.