Add the lentils, coconut milk, and 1 to 2 teaspoons kosher salt (Note: if you are sensitive to salt or using table salt or even Morton’s kosher salt, which is saltier than Diamond Crystal kosher salt, start with 1 teaspoon, then add more to taste—I use Diamond Crystal and so typically use 2, but use your judgement), then fill the empty coconut-milk can with water and add it to the saucepan. It will look like a lot of liquid, but the lentils will absorb it as they cook. Stir everything together, turn the heat to high, and bring the mixture to a boil. Turn the heat to low and let the lentils simmer, stirring now and then, until they’re completely soft, about 20 minutes. Season to taste with salt. (Note: If you’re using French green lentils, you will need to cook this longer, 30 to 45 minutes. Just keep tasting to see when the lentils are cooked through. You may or may not need to add more water.)