In a large iron skillet sauté the onion with one tablespoon of the oil until tender then add the mushrooms and continue over medium heat adding more oil as needed. Then add in the diced zucchini, salt, pepper and onion powder and continue to cook over medium, stirring occasionally. Put a lid over the pan and allow to cook for 10 minutes before adding first the swiss chard, let that cook down a bit and then add the tomatoes and replace lid.
When all veggies are tender, probably about 5 minutes after adding tomatoes it is ready to serve and enjoy. You can substitute oil for either butter or bacon grease if you choose. This does keep well in the frig for leftovers the next day.