Bring a large pot of well-salted water to a boil. Add couscous and cook 8 to 10 minutes, until couscous has puffed up and is cooked through to the center. Drain and allow to cool. Transfer to a large bowl.
Prepare dressing by whisking together the lemon juice and mustard while drizzling in the olive oil. Once slightly emulsified, stir in pepper flakes and season with salt and cracked black pepper.
Toss the tomato, currants, cucumber, red bell pepper, onion and arugula with the couscous. Pour the dressing over top. Season with salt and pepper to taste and toss to the combine.