Place a large pot over medium heat and add the olive oil, garlic and chillies. Sauté for 1 minute, until garlic is fragrant, then add the green capsicum and cook for a further 2 minutes.Add the tomato paste and stir for about 30 seconds. Add the can of tomatoes and stir well. Fill the empty can with water till about two thirds full, swish the water around to collect any residual tomato, then add that to the pot. Add the sugar and season with salt & pepper, bring to a low simmer and cook, partially covered for 20-25 minutes, stirring occasionally until thickened substantially.Have a taste and adjust seasoning. At this point, you can cool and store the sauce in an airtight container in the fridge for up to 3 days.When ready to serve, boil the penne till al dente, then toss with the (hot!) sauce in the pot for a minute or two until all the pasta is nicely coated, If the sauce is too thick, add some of the pasta’s cooking water to loosen it up to desired consistency. Serve immediately.