How to Make It
In a large saucepan, cover the farro with 2 inches of water. Bring to a boil and simmer over moderately low heat until the farro is al dente, about 25 minutes. Drain the farro and spread it out on a baking sheet to cool completely.
Meanwhile, in a medium saucepan of salted boiling water, cook the peas until tender, 3 to 5 minutes. Using a slotted spoon, transfer the peas to a sieve and cool under running water. Add the onions to the saucepan and blanch just until the skins start to wrinkle, 1 to 2 minutes. Drain the onions and cool them under running water, then peel them.
Preheat a grill pan. In a large bowl, toss the onions with 1 tablespoon of the olive oil and season with salt and pepper. Grill the onions over moderately high heat, tossing occasionally, until they are softened and charred in spots, about 8 minutes. Return the onions to the bowl and let them cool. Add the cooled farro, peas, lemon juice and the remaining 1/4 cup of olive oil. Fold in the feta, mint and oregano, season the salad with salt and pepper and serve.