Heat 2 Tbsp. oil in a large nonstick skillet over medium-high until very hot but not smoking. Season bass with salt and pepper and cook, skin side down, gently pressing occasionally with a spatula to ensure contact with skillet, until skin is browned and crisp and flesh is nearly opaque, 6–8 minutes. Turn and cook until flesh is opaque throughout, about 1 minute longer.
Meanwhile, toss scallions, chile, cilantro, lime juice, sesame seeds, and remaining 2 Tbsp. oil in a medium bowl; season with salt. Serve bass with scallion-chile relish.
