Heat olive oil over medium-high heat in a large ovenproof saucepan or dutch oven. Sauté the onions until they turn soft and translucent, about 4–5 minutes. Add garlic, salt, pepper, and red pepper flakes, cooking until fragrant, about 30 seconds. Stir in farro and cook for 1 minute. Add wine, letting it bubble until the farro absorbs it.