Preheat the oven as directed on the package of your ready-to-bake flatbread.
Roll out the flatbread onto parchment and place it onto a baking sheet. Some ready-to-bake flatbreads come prepared with parchment; you can use that.
Carefully slice the asparagus spears in half lengthwise. Transfer them to a large mixing bowl and drizzle them with a bit of olive oil; season with a pinch of salt and pepper. Using your hands, toss the asparagus to coat. Set the bowl aside.
Evenly spread the ricotta over the dough leaving some space along the edges for a crust.
Place the spears over the flatbread in rows followed by the flaked chunks of the mackerel.
Bake the flatbread into the oven and bake for the time noted in the directions on the package. When the flatbread is ready, remove it from the oven and sprinkle lemon zest over the entire flatbread.
Distribute the sliced radishes over the top of the flatbread and squeeze a generous amount of lemon juice over it all. Finish it off with chopped fresh parsley for presentation's sake if you'd like.
Cut the flatbread into squares and enjoy!