01 - Preheat the oven to 300°F. Line a rimmed baking sheet with parchment paper.
02 - Arrange halved tomatoes cut side up on the prepared sheet. Drizzle with olive oil, sprinkle with salt, pepper, oregano, and scatter garlic slices over. Roast for 1½ hours, until tomatoes are deeply caramelized and shriveled but still moist. Let cool.
03 - Rinse farro under cold water. Combine farro, water, and salt in a medium saucepan. Bring to a boil, then reduce heat and simmer for 25–30 minutes, until farro is tender but chewy. Drain any excess water and let farro cool to room temperature.
04 - In a large bowl, whisk together olive oil, red wine vinegar, Dijon mustard, honey, salt, and pepper for the dressing.
05 - Add cooled farro, slow-roasted tomatoes with their juices, red onion, basil, parsley, and arugula to the bowl. Toss gently to combine and coat everything in the dressing.
06 - Top with crumbled feta. Toss lightly and serve at room temperature or slightly chilled.