Preheat the grill, scrape it well.Whisk together the olive oil, red wine vinegar, maple syrup, salt, cinnamon and pepper, reserve.
Build a salad on a platter with lettuce on the bottom, then sprinkle with mint and scallions.
Use a paring knife to cut the plums in half, cutting them away from the pit. Place on a plate, skin side down, and brush with avocado oil.Use tongs to dip a wadded paper towel in avocado oil and brush the hot grill, then place the plums, cut side down, on the hot grill. Grill for 2-3 minutes, until marked and softened. Use tongs to turn the plum halves, then cook for a couple of minutes to finish cooking. Transfer to a plate to cool.
To serve, arrange the plums over the salad and sprinkle with pistachios, drizzle with dressing. Serve immediately.