Boil the kettle and turn on the hob on full. As your wait on the kettle, half fill your pot with pasta and a little salt and pepper. Then when the kettle is done pour it into your pot and place it on the hob. Add a little dribble of oil (it stops the pasta sticking together).
As the pasta is cooking turn on the oven to full. At this point you could crush your crisps, grate your cheese and have your mustard, butter and tuna ready.
When your pasta is done drain it and pop it back in the pot. Add your butter, salt, pepper and mustard, and mix it all up (off the heat). Add your sauce to taste, mix a little, then place it back on the hob and add your tuna and cheese. Mix well.
Then place it in a baking dish and sprinkle the crisps on top.
Bake in the oven about 10 to 20 minutes.
I am lazy and get the tomato and bacon pasta sauce from Aldi.