The star of this dish is the juicy grapefruit that gets tossed with this noodle salad. The residual juice gets used in the dressing as well, giving the whole salad a tart and refreshing flavor. Don’t skip the crispy shallots! They add a delicious savory crunch.
Bring a large pot of water to a boil. Trim the top and bottom of the grapefruit, then slice off the peel and white pith. Hold the grapefruit over a bowl and cut out the segments, letting them drop into the bowl; tear into bite-size pieces. Squeeze the juices from the membranes into the bowl.
Make the dressing: Remove 2 tablespoons of the grapefruit juice to a large bowl. Stir in the fish sauce, all but 1 teaspoon of the chili sauce, 1 teaspoon ginger, the lime juice and 2 tablespoons water.
Heat the vegetable oil in a large nonstick skillet over medium-high heat. Add the shallots and cook, stirring, until starting to crisp, 3 to 4 minutes. Remove the shallots to a paper towel–lined plate to drain. Pour the oil from the skillet into the fish sauce dressing, leaving a coating of oil in the skillet.
Season the shrimp with salt and pepper in a bowl. Toss with the remaining 1 teaspoon chili sauce and 2 teaspoons ginger. Add the shrimp to the skillet and cook over medium-high heat, stirring, until cooked through, 1 to 2 minutes per side. Remove to a plate.
When the water comes to a boil, remove from the heat and submerge the noodles; stir until tender, 3 minutes. Drain in a sieve and rinse under cold water; shake out as much water as possible.
Toss the noodles, slaw mix and mint with the dressing. Divide among bowls. Top with the shrimp, grapefruit and shallots.