How to Make It
Stir together tangerine rounds, 1/2 cup tangerine juice, and 1 tablespoon salt in a small saucepan. Bring to a boil over high. Cook, stirring occasionally, until salt is dissolved. Reduce heat to low; cover and simmer until citrus peels are tender, about 10 minutes. Remove from heat, and let cool 10 minutes. Remove 5 tangerine rounds from juice, allowing excess juice to drip off; cut rounds into quarters. Set quarters aside.
Gently stir together parsley, 1/4 cup oil, shallot, crushed red pepper, tangerine quarters, 1 1/2 teaspoons cooked tangerine juice, and remaining 2 tablespoons fresh tangerine juice in a small bowl; set aside.
Heat remaining 1 1/2 tablespoons oil in a large skillet over medium-high. Season snapper fillets evenly with remaining 1 teaspoon salt. When oil is very hot, add snapper fillets, skin sides down. Immediately press fillets gently with a spatula until skin stays flat in skillet. Sear until skin is browned and crisp, 5 to 7 minutes. Flip fillets; cook until bottom half of flesh is opaque, about 30 seconds. Transfer fillets to 4 plates; spoon gremolata over fillets, and serve with fregola sarda.
Use organic citrus whenever possible, and scrub any waxy residue off peels before preserving.