Bring a large pot of salted water to a boil. Cook pasta for 8–10 minutes until al dente. Reserve a cup of pasta water, drain, and set aside.

Heat olive oil in a skillet over medium heat. Sauté onion and garlic for 2–3 minutes until soft and fragrant.

Stir in tomato paste, then add canned tomatoes, Italian seasoning, salt, pepper, and optional sugar. Simmer for 3–5 minutes until thickened.

If using spinach, add it during the last minute of simmering and stir until wilted.

Add drained pasta to the sauce, tossing gently. Adjust sauce consistency with reserved pasta water if needed. Heat through for 1–2 minutes.

Serve immediately, garnished with grated Parmesan and fresh herbs if desired.