Preheat an outdoor or indoor grill to high. Soak wooden skewers in water for 5 minutes. Combine the lemon, orange and lime zest and juice in a large bowl with the coriander, red pepper flakes, garlic and EVOO. Slide the chicken strips in the marinade and let them for at least 10 minutes, but no longer than 30 minutes.
While the chicken is marinating, make the sauce: In a medium bowl, combine the grated cucumber flesh, yogurt, red onion, coriander, lemon and lime juices. Season with salt and pepper. If the sauce is too thick, use some of the reserved cucumber juice to thin it out a bit.