In a large deep skillet or pot, heat olive oil over medium heat. Add garlic and onion; sauté for 2–3 minutes until fragrant and soft.
Stir in cherry tomatoes, then pour in the linguine and broth. Add red chili flakes, a pinch of salt, and pepper. Bring to a boil, then reduce heat and simmer uncovered for about 10–12 minutes, stirring often until the pasta is al dente and most liquid is absorbed.
Add lemon zest and juice if using.
Add the spinach and stir until wilted (1–2 minutes). Turn off heat, then gently stir in ricotta cheese and Parmesan until creamy.
Adjust seasoning as needed. Top with extra ricotta dollops, herbs, and a sprinkle of black pepper. Serve warm!
