In a large pot, bring 5 cups water, 1 1/2 tsp coarse salt, the farro and chile to a boil. Reduce to a simmer, cover and cook until the farro is tender, about 25 minutes. Drain, then discard the chile. Transfer the farro to a large bowl and refrigerate until cold.
Meanwhile, in a medium bowl, whisk together the garlic, lemon zest, vinegar and mustard. While whisking, drizzle in the EVOO. Season with salt and pepper.
Using a small, sharp knife, carefully cut away the remaining peel and white pith from the zested lemon. Cut out the segments and slice them into small pieces. Toss the lemon pieces with the cooked farro, cucumber, arugula, tuna, shallot and mint. Drizzle the salad with the dressing and toss again. Sprinkle with the goat cheese.