Preheat oven to 425 degrees. Move oven rack to the upper third of your oven.

Use a peeler or zester to remove the zest of one lemon and set aside.

With a sharp paring knife, carefully cut asparagus into long, thin strips (halved or quartered, depending on the thickness). Slice radishes paper-thin. Toss asparagus and radishes with 1 tablespoon freshly squeezed lemon juice and a generous pinch sea salt, and set aside.

In a small bowl, whisk to combine 1 teaspoon lemon juice, 1 teaspoon olive oil, and a pinch sea salt. Toss dressing with mizuna and set aside.

In a small bowl, stir remaining 2 tablespoons lemon juice into ricotta. Add sea salt and pepper to taste.

Place flatbreads on 2 rimmed baking sheets (or just 1 if they'll fit), brush with olive oil, then layer mizuna and asparagus strips, and tuck radishes throughout. Scatter lemon zest over the top.

Slide flatbreads into oven and bake just until vegetables have wilted slightly and breads are golden, 2 - 4 minutes.

Dot ricotta mixture all over hot flatbreads. Drizzle remaining olive oil over the cheese and vegetables. When cool enough to handle, slice into triangles and serve.