1. Cut the avocados in half. With the tip of a small knife, loosen the seeds and lift them out. Remove any brown tissuelike fibers clinging to the flesh.
2. Starting at the narrow stem end, strip off the skin with your fingers or with a small knife. Cut the avocado into ¼-inch cubes and drop them into a bowl. Pour in the lemon juice and turn the cubes about gently with a spoon until they are evenly coated.
3. Add the tomatoes, chili, vinegar and oil, and toss together gently but thoroughly. Taste and season with salt, then let the sauce rest at room temperature for about 30 minutes before serving.
4. Poor man's butter is traditionally served as a spread for hot tortillas, and is also used as a filling for tacos or topping for tostadas.
