For a milder sauce, be sure to remove the seeds and membranes from the jalapeño peppers before slicing. For extra heat, leave some seeds in! Adjust spice levels to your liking. If you don't have fresh tomatoes, you can substitute a 28-ounce can of crushed tomatoes. Be sure to adjust cooking times accordingly. Garnish with avocado slices or a dollop of sour cream for an extra layer of richness. Leftovers can be stored in the refrigerator for up to 3 days. Reheat gently on the stovetop or in the microwave.