As the pasta boils, make the sauce: In a large skillet (large enough to accommodate the pasta), heat oil over medium heat. Add garlic and cook until fragrant and tender, stirring occasionally, 2-3 minutes. Carefully add the reserved pasta cooking water in a slow stream, and simmer until water has reduced by about a third, about 5 minutes. Lower the heat and stir in 1/2 teaspoon table salt, lemon juice, lemon zest, and cooked pasta, and toss. Remove from heat and stir in cilantro and Parmesan (start with ½ cup and add more as you wish).