Brush the cut-side of your peaches with olive oil and sprinkle with the tiniest pinch of salt.
Heat a lightly oiled grill or grill pan over medium-high heat. When hot, place the peaches on the grill cut-side down and cook for about 5 minutes until slightly softened with visible grill marks.
Meanwhile, heat a small saucepan over medium-low heat. Add the honey and cinnamon and cook for about 45 seconds, stirring regularly, until warmed through.
To assemble your sundaes: Put the grilled peach halves into bowls or fancy serving plates. Top each half with a scoop of vanilla ice cream, sprinkle with granola and drizzle with the cinnamon-honey. Serve immediately.