Toast 1/3 cup slivered almonds in a skillet with olive oil; season with 1/2 teaspoon ground cumin and a pinch each of cayenne and salt. Drain on paper towels. Toss 2 cups each cubed cantaloupe and honeydew melon with 1/4 cup each olive oil, thinly sliced red onion and chopped mixed parsley and mint, and 2 tablespoons white balsamic vinegar; season with salt and pepper. Top with the almonds.