Cook the Pasta: Bring a large pot of salted water to a rolling boil. Add the spaghetti and cook according to package directions until just tender but still firm to the bite (al dente). Before draining, scoop out 1 cup of the pasta water and set aside. Drain the pasta thoroughly.
Infuse the Olive Oil: While the pasta cooks, heat the olive oil in a spacious skillet over medium heat. Add the thinly sliced garlic along with the crushed red pepper flakes. Stir frequently and cook for about 30 seconds to 1 minute until the garlic edges turn a delicate golden brown, releasing an aromatic fragrance. Be careful not to burn the garlic.
Sauté the Kale: Add the chopped kale to the skillet along with the sea salt and a few grinds of black pepper. Toss with tongs and sauté for up to 1 minute, just until the kale softens and wilts, maintaining a vibrant green color.
Combine Pasta and Sauce: Transfer the drained spaghetti into the skillet with the kale and garlic oil. Toss thoroughly to coat the noodles. Pour in ½ cup of the reserved pasta water, then add the fresh lemon juice and zest. Continue to toss, allowing the pasta water to emulsify with the oil, creating a silky, light sauce. If the pasta seems dry, gradually stir in the remaining pasta water until the desired consistency is reached.
Final Seasoning and Serve: Taste and adjust seasoning with additional salt and pepper if needed. Remove from heat and sprinkle with chopped parsley. Serve immediately, topped with grated Parmesan or vegan Parmesan cheese.