01 - Preheat the oven to 300°F. Line a rimmed baking sheet with parchment paper. Arrange halved tomatoes cut side up on the prepared sheet.
02 - Drizzle tomatoes with olive oil, then sprinkle with salt, pepper, and oregano. Scatter garlic slices over the top. Roast for 1½ hours until tomatoes are deeply caramelized and shriveled but still moist. Allow to cool.
03 - While tomatoes roast, 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 cool to room temperature.
04 - In a large bowl, whisk together olive oil, red wine vinegar, Dijon mustard, honey, salt, and pepper until fully emulsified.
05 - Add cooled farro, slow-roasted tomatoes with their juices, red onion, basil, parsley, and arugula to the bowl with dressing. Toss gently to combine and coat everything evenly.
06 - Top with crumbled feta and toss lightly. Serve at room temperature or slightly chilled.