Soak the farro in water for 25 minutes. Drain.
Bring a pot of salted water to a boil. Add the farro and reduce to a gentle boil and cook about 15-20 minutes until just tender.
Drain and rinse with cold water. Add a small spoonful of olive oil and stir to coat the grains. Set aside.
When the farro is completely cool, add the onion, fennel, cucumber, fennel fronds and parsley.
Stir in the vinegar and oil and season with salt and pepper to taste. (Note salad can be made to this point and refrigerated overnight).
To serve. Check seasoning and add more salt if needed. Stir in the arugula and tomatoes and cheese.
Transfer to a bowl and serve immediately.
Note: if you make this salad ahead it will be necessary to re-season aggressively with salt and possibly another spoonful of vinegar.