Preheat barbecue to medium heat. In a bowl, mix peach slices, blueberries, brown sugar, lemon juice and cinnamon. Spread the mixture in a 10-in. (25 cm) cast-iron pan or two stacked (13 × 10-in./32 × 25 cm) rectangular disposable aluminum pans.
Mix pecans in a large bowl with flour, brown sugar, thyme and salt. Grate the chilled butter into the bowl. Use fingertips to rub the butter into the flour mixture until it resembles coarse meal. Sprinkle evenly over fruit. Set on the grill and cook for 20 to 25 min. or until the topping is golden brown and the fruit is bubbling. Cool slightly before serving.