Place most of the cilantro into a blender, reserving the rest for garnish. Add sour cream, lime juice, jalapeno, and salt. Blend until just liquefied. Place sauce in refrigerator until ready to use.
Preheat the grill for medium heat and lightly oil the grate.
Sprinkle tilapia fillets with onion powder, herbes de Provence, pepper, chives, and salt. Grill tilapia until fish flakes easily with a fork, 4 to 6 minutes.
Place each tortilla between 2 damp paper towels. Heat in the microwave, about 20 seconds.
Shred tilapia and arrange down the center of each tortilla. Squeeze lime juice over tilapia and top with cabbage and red onion. Spoon the cilantro sauce over the tacos and top with queso fresco. Garnish with the reserved cilantro.