Cook the farro as the label directs. Meanwhile, whisk the orange juice, vinegar and olive oil in a large bowl; season with 1/2 teaspoon each salt and pepper. Add the plums, fennel, shallot and jalapeño and toss well to coat.
Preheat a grill to medium high and oil the grates. Toss the scallops with the coriander, orange zest and 1/4 teaspoon each salt and pepper. Grill the scallops until browned, about 2 minutes per side. Transfer to a large plate.
Fluff the farro with a fork and add it to the plum-fennel mixture. Stir in the mint. Divide the farro salad among plates and top with the scallops.