First, get your pasta water on the stove in a large pot and bring it to a boil.
While the water is coming to a boil, heat olive oil in a medium sauté pan on medium-low heat. Add the garlic and onion. Cook, stirring frequently until the onion has softened and become translucent, about 4 minutes. Be careful not to brown the garlic. Season with a pinch of sea salt. Add the tomatoes and stir to coat. Cook on medium-low heat for 5-8 minutes, the tomatoes have started to break down just ever so slightly and some of their juice has mixed with the oil. Remove from the heat and taste. Season with salt if necessary.
Once the water is boiling, season it with sea salt and add the pasta. Cook until al dente. Once the pasta is finished, scoop it directly from the boiling water into the saucepan, stirring it to coat. Add a handful of torn basil leaves and stir. If it appears dry for any reason, you can add a little pasta water to help loosen it up. Taste and season with salt if necessary. Serve immediately.