Begin by finely chopping the onion, chili, garlic and parsley and setting them aside.
Open the canned tomatoes and take each tomato and remove the seeds. While your doing that you can also pull out any yellow fibrous core you might find. Both the seeds and this stringy fiber helps makes your sauce more acid which you don't want. This is an extra step but I think it is worth it. Keep all the liquid from the can in a bowl. When all the seeds have been removed chop the tomatoes coarsely and add to the tomato liquid from the cans.
Heat a large frying pan with 3 to 4 tbps. olive oil and let it get hot. When hot toss in the onions and cook until translucent, then add the chopped chili and cook for 1 minute, add the garlic and cook for 30 seconds (don't let it burn) then add 3 of the 4 tbsp. of chopped parsley and stir in well and cook for one more minute, still taking care not to burn the garlic.
Add the tomatoes and bring back up to a high heat. At this time add salt, sugar and a really good grinding of freshly ground pepper and cook for 8-10 minutes.
Most of the excess water from the tomatoes should have evaporated.
Add the shrimp and cook until they have turned pink, it shouldn't take more than 4 or 5 minutes.
When the pasta is done drain and add to the pan containing the sauce and shrimp. Toss well to coat all the pasta. If the sauce is too thick you can thin it will a little warm water.
In 2 warmed bowls plate the pasta then drizzle over 1 tbsp. of the olive oil over each plate.
Place the sauced pasta on a heated serving plate, sprinkle on the remaining chopped parsley and drizzle over the remaining 2 msk, (2tbls.) olive oil.