Yeah... its probably over-exposure to sun... however, you say that you were over-watering and have now cut back, but at the same time you say that the temps have increased. When the days are really hot and plants get 10 hours of direct sun it is nearly impossible to over-water a raised bed. You could need to water them a little more (in the morning or evening). To be honest that type of leaf curle reminds me of the plants I had growing at my mom's house. I had made a "pepper mound" that had excellent drainage and really rich soil. The bed received absolutely full sun and she did not water it very often. The resulting plants looked exactly like those you have. Ill bet they are rally hard to the touch and waxy feeling???