Pulse the onion, garlic and chilli together in a food processor until finely chopped and place them in a frying pan with a tightly fitting lid. Add the lardons and a good pinch of salt. Sweat on a low heat for 20-30 minutes, stirring occasionally, until the onions have completely melted.
While the onions are cooking, beat the grated parmesan and eggs together in a medium-sized bowl and season well with salt and pepper.
Cook the pasta according to packet instructions in plenty of well-salted water. Two minutes before the end of the cooking time, take a ladle of the starchy pasta cooking water and add this to the parmsesan and egg mixture.
Now add the peas to the pasta water for the final minute. When the pasta is cooked, drain thoroughly and add it back into the pan. Working quickly tip the parmesan and egg mixture over the pasta and keep stirring and tossing, the sauce will take a minute or so to emulsify. Do not overheat or the eggs will scramble.
Tear the mint, scatter generously and serve.