Preheat the grill over medium-high heat to about 375 degrees F or preheat a large grill pan over medium heat. Clean the grill grates.
Grill the corn, flipping occasionally, until you see grill marks and the corn turns bright yellow, 8 to 10 minutes. Remove and let cool slightly.
Meanwhile, combine the shrimp with the lemon zest, a drizzle of grapeseed oil and a sprinkle each of salt and pepper in a medium bowl. Toss together. While the corn is cooling, grill the shrimp until you see grill marks and the shrimp is pink, 1 to 2 minutes per side.
Once the corn is cool enough to handle, cut the kernels off the cob and place into a large bowl; discard the cobs. Add the snap peas, chopped mint, radishes, almost all of the scallions (save the rest for garnish), the lemon juice, a drizzle of the olive oil and a sprinkle each of salt and pepper. Toss together and taste for seasoning. Add the feta and shrimp and toss to combine.
Serve in a large shallow dish and sprinkle with the reserved scallions and mint leaves. Serve at room temperature or slightly chilled.