Set water to boil on the stove for the pasta.
While the water starts to boil, prepare the vegetables. Dice the white onion, celery, carrots, and spinach and add them to a large mixing bowl.
Add the frozen peas and corn, as well as the tuna, to the mixing bowl and incorporate the ingredients. Flake the tuna to make sure it mixes evenly.
Drain the boiled pasta and pour the hot pasta onto the vegetable and tuna mixture in the mixing bowl.
Mix it all up and check the frozen peas and corn to make sure they thawed (the hot pasta should take care of that).
Add a dollop or two of mayonnaise (~2 tablespoons) to the bowl and mix. If it looks like you need more, then add another spoonful.
Top the mixture off with some salt and pepper.
Refrigerate the pasta salad until chilled.
