Heat the olive oil in a large nonstick skillet over medium-high heat. Add the oregano and garlic; saute for 30 seconds. Add the tomatoes, green onions, 2 tablespoons parsley, and lemon juice: cook 2 minutes or until thoroughly heated.
Combine the tomato mixture, cooked spaghetti, and ¾ cup cheese; toss gently. Top with the remaining cheese and parsley and serve with freshly ground black pepper.
Garnish with lemon slices and green onions, if desired.