Whisk 3 tablespoons vegetable oil, 1 tablespoon each fresh lime juice and orange juice, 1 minced shallot and 1/2 teaspoon salt in a large bowl. Add 2 diced avocados, 1 1/2 cups cubed jicama or radishes, 1/2 cup each cubed mango and pineapple and 2 tablespoons chopped cilantro; gently toss. Season with salt.