Cook pasta according to package instructions; drain. Stir in pesto until well coated. Gently fold in cherry tomatoes and mozzarella; set aside.
Heat the olive oil in a large fry pan over medium heat. Cook the sea bass, skin side down, until the skin is crisp, about 5 - 7 minutes. Flip the fish over and continue frying until cooked through, about 5 minutes.
Place the pesto spaghetti on a plate and top with the sea bass.