Peel 1 jicama (1 1/4 pounds) and cut into thin matchsticks. Cut 4 radishes into matchsticks. Whisk 3 tablespoons olive oil, 2 tablespoons lemon juice, 2 teaspoons agave syrup, 1/2 teaspoon kosher salt and a pinch of cayenne pepper in a large bowl. Add the jicama, radishes, 1 sliced scallion and 2 tablespoons each chopped cilantro and mint; toss. Season with salt.