If you can’t find bay scallops, which are small, buy a pound of sea scallops and cut them into quarters.
Trim off ends of oranges; set oranges, cut side down, on a cutting board. Following the curve of the fruit, cut off peel and white pith. Working over a medium bowl, slice orange segments from membranes; cover and refrigerate. Squeeze juice from membranes into a separate medium bowl to equal 3/4 cup; discard membranes. Add scallops and 6 tablespoons of the lime juice to bowl with orange juice. Cover and refrigerate until scallops are opaque, about 45 minutes.
Drain scallop mixture; discard liquid. Place scallops in a clean bowl. Stir in orange segments, watermelon, fennel, jalapeño, honey, salt, lime zest, and remaining 2 tablespoons lime juice. Drizzle with oil and top with mint. Serve with a slotted spoon.