Prepare the pasta as per packaging instructions in salty water. Reserve 1/4 cup of pasta water.
Pan-fry the bacon in sections over medium heat, being careful not to overcrowd the pan. Remove the bacon and roughly chop it. Save it for later use.
Remove 3/4 of the bacon grease and reserve it for later use. In the remaining bacon grease, sauté the onions with a pinch of salt. Cook for 4-6 minutes until the onions have sweated out and become soft.
Add the peas and cook for 1-2 minutes.
Add in the bacon and toss.
Add pasta, parmesan cheese, 1 tbsp of the bacon fat and 1-2 tbsp of pasta water. Toss and serve.