Bring a large pot of salted water to a boil. Add the pasta and cook until al dente. Reserve ¼–½ cup of the pasta water, then drain.
Heat olive oil in a pan over medium heat. Add the onion and cook until soft and lightly golden.
Add the garlic and stir for about 30 seconds, just until fragrant. Remove from heat.
Add roasted red peppers, onion, garlic, Greek yogurt or white beans, nutritional yeast, lemon juice, smoked paprika, salt, and pepper to a blender.
Blend until smooth. Add a little reserved pasta water if the sauce feels too thick.
Return the pasta to the pot. Pour the sauce over the pasta and toss gently to coat.
Add more pasta water if needed until the sauce is creamy and glossy.
Taste and adjust seasoning. Serve warm with herbs, parmesan, or chili flakes if desired.