In California it usually cools off in the evening, so I cook chicken or roast meat and serve it cold the next day. Potato salad can be made ahead and served cold and I use my microwave to cook as much as possible - it really keeps the kitchen cooler than the oven and stove. Cold soup, such as gazpacho, is also good. Actually, if you adjust your cooking for the coolest part of the day, you can just heat the meal in the microwave later.