1 pound flat-leaf kale (about 2 bunches)
1/3 cup olive oil
1 teaspoon kosher salt, plus more as needed
2 medium garlic cloves, finely chopped
2 tablespoons cider vinegar
2 teaspoons Dijon mustard
12 ounces red or yellow cherry tomatoes, halved
6 ounces feta cheese, crumbled (about 1 1/2 cups)
2 medium scallions, thinly sliced (white and light green parts only)
2 tablespoons thinly sliced fresh mint leaves