In a large bowl, whisk together lime juice, honey, oil, and salt; set aside.
Cut each cantaloupe quarter in half lengthwise. Run a knife between the flesh and the skin of the melon; discard skin. Slice each wedge lengthwise into 1/2-inch pieces.
Cut each avocado half again length-wise and then into 1/2-inch-thick slices. Add cantaloupe, avocado, and grape tomatoes to bowl with dressing and toss to coat. Divide among 4 plates.