Whisk together the mayonnaise, half of the lemon juice, and 4 tablespoons of parsley in a small bowl. Season with salt and pepper to taste. Set aside.
Heat the vegetable oil in a large pan until it reaches 350°F.
Bring a pot of salted water to a boil for the pasta.
Prepare the tempura batter as per the box instructions, using 1 cup of ice water. Slice the calamari into rings and dip them, along with the tentacles, into the tempura batter.
Fry the calamari in the preheated oil for 2-3 minutes or until the batter is puffed and golden. Remove to a plate lined with paper towels to drain.
Melt the butter in a skillet over medium heat. Add the sliced onions, red peppers, and minced garlic, sautéing until softened.
Cook the angel hair pasta in the boiling water for 4-5 minutes or according to package instructions for al dente.
Drain the pasta, reserving one cup of the pasta water.
Add the cooked pasta to the skillet with the peppers, onions, and garlic. Pour in the reserved pasta water and the prepared mayonnaise/lemon sauce. Stir until the noodles are evenly coated.
Mix in the shredded Parmesan cheese, and season with additional lemon juice and salt and pepper to taste. Garnish with additional parsley. Serve with extra Parmesan cheese sprinkled on top and enjoy!