Heat the oil in a large saucepan over high heat. Add the sausages and enough water to come about half way up the sausages. Cover, reduce the heat to medium low, and cook until done, about 10 minutes. Remove the lid and allow the water to evaporate. The sausages will then fry in their oil when water evaporates. Remove the sausages from the saucepan and drain them on paper towels. Remove all but 2 tablespoons of fat from the saucepan. Add the sliced garlic and chiles and cook until the garlic begins to brown, about 1 minute, stirring occasionally. Add the basil and cook for 15 seconds, then add the tomato puree. Simmer the mixture for 15 to 20 minutes, stirring occasionally. Taste and adjust seasoning with salt and pepper.
Cut the sausage links in half lengthwise, then crosswise into 1/4-inch pieces, creating half-moons. Return the sausages to the saucepan and heat through.