I like the idea, but if a kid got a tomato with their meal, they wouldn't understand. They'd ask the parent what it is and why they got it. If the parent doesn't get it, then the tomato ends up in the bin. I feel this has to start with parent education or it's just going to end in more food wastage.
McDonalds in Australia already offers apple slices with their happy meal instead of chips and juice instead of coke and has done this for about 2 years. I wonder how well that's going. I know my kids are happy with the juice whenever they have it, but they always want to have the chips instead of apple.