Wash the green tomatoes or tomatillos, zucchini, chili peppers, and garlic.
Cut the tomatillos into quarters and the zucchini into large pieces.
Heat a pan over medium heat and add the oil.
Add tomatillos, zucchini, chili peppers, and garlic to the pan. Sauté the vegetables for about 10 minutes, stirring occasionally, until they are soft and slightly golden. Add water to help loosen any vegetables stuck to the bottom of the pan. Remove the pan from the heat and let the vegetables cool for a few minutes.
Transfer the vegetables to a blender or food processor. Add the cilantro and a pinch of salt to the blender or food processor. Blend until you have a smooth and homogeneous sauce. Taste the sauce and adjust the salt as necessary.
Serve the Mexican green sauce immediately or store it in an airtight container in the refrigerator for up to 3 days.