Brush peach halves with softened butter. Grill over medium-high heat 5-8 minutes, turning once until nicely charred on the outside. Transfer peaches to a cutting board and let cool slightly. Once cooled, slice into wedges. Set aside.

In a large serving bowl, combine cherries and arugula. Arrange grilled peach wedges over top and set aside.

Make the vinaigrette. Place raspberries in a small bowl and sprinkle with sugar. Let stand 5 minutes then mash thoroughly until smooth. Transfer mashed raspberry to a jar with a tight-fitting lid. Add vinegar, oil, agave, and salt to jar and screw on lid. Shake thoroughly until smooth. Add a little more agave if the dressing is too tart.

Drizzle dressing over salad and toss to combine. Serve salad immediately.