For the fish: Preheat a broiler. Spray a small baking sheet or flameproof baking dish with vegetable oil cooking spray. Set aside.
Drizzle the tilapia fillets on both sides with olive oil and season with salt and pepper. Arrange the fillets in a single layer on the prepared baking sheet and broil until cooked through and the flesh flakes easily with a fork, about 6 to 8 minutes. Set aside to cool slightly.
For the sauce: In a small bowl, mix together the yogurt, agave nectar, and mustard until smooth. Whisk in the lemon juice and chives. Season with salt and pepper, to taste.
Transfer the tilapia to a serving platter and drizzle with the sauce.