Cook spaghettini or spaghetti until al dente. Reserve pasta water!
While pasta is cooking, add oil to a large, deep-sided pan over medium-high heat.
Once the oil is shimmering, carefully add zucchini.
Fry zucchini until slightly golden brown. Transfer to a paper towel-lined plate and season with sea salt.
Remove a few tbsp of oil with a large spoon.
Add chili flakes and onion to the pan. Cook for 2-3 minutes.
Stir in garlic and cook for 1 minute.
Add in sardines (including the oil). Use your tongs or spatula to break up the sardines.
Add rinsed beans, parsley and zucchini. Toss to combine.
Add lemon juice and a few ladles of pasta water to emulsify.
Add as much parmigiano as you wish. If needed, add another ladle of pasta water.
Check for seasoning and serve.