Prepare a grill for medium heat; oil grate. Pulse coconut flakes in a food processor or a blender until coarsely chopped. Finely grate lime zest directly onto halibut and pack on coconut flakes. Drizzle lightly with oil; season with salt and pepper. Lightly coat bok choy with 1 Tbsp. oil; season with salt. Grill halibut, turning once, until browned on both sides and just opaque in center, about 5 minutes.