Heat the olive oil in a large, heavy-bottomed pot over medium-high heat.
Add the scallion whites, 1 teaspoon salt, and a few grinds of black pepper. Cook for 3 to 4 minutes until softened and caramelized.
Mix in the oregano, red pepper flakes, and garlic, stirring for about 1 minute until fragrant.
Add the lemon juice, 5 1/2 cups water, and another teaspoon of salt. Scrape any browned bits from the bottom of the pot.
Place the spaghettoni in the pot, spreading it out as evenly as possible. Bring the water to a boil.
Cook, stirring frequently to prevent sticking, for 10 to 12 minutes until the pasta is al dente and the water is mostly evaporated.
Turn off the heat and stir in the Parmesan, ricotta, and lemon zest until the sauce becomes creamy.
Divide into four bowls, topping with scallion greens and fresh black pepper. Serve immediately!