Preheat oven to 400 F.
Using a very sharp knife, cut tuna steak into small, diced pieces. To make this easier, you can either freeze tuna for about an hour to make cuts more precise, or if using frozen tuna you can start cutting before it's been fully defrosted.
Prepare kiwifruit and veggies and toss with lime juice and salt, letting stand for at least 15-20 min for flavours to absorb.
Meanwhile, place wonton wrappers in a greased 24-count mini muffin tin, pressing to create a flat surface at the bottom of each cup. Bake in the oven for 7-10 min, watching so they don't burn.
Remove shells when they are firm but not overly browned. Add tuna to the kiwi avocado salsa and toss. Distribute mixture evenly among wonton shells.
Serve immediately, and if not serving immediately then keep tuna and kiwi salsa mixture separate until ready to serve.