1. Fill a bowl with ice and water and set on the counter. Fill a large pot with 1 inch of water and bring to a boil over high heat. Insert a steamer, add the asparagus, cover the pot and reduce the heat to low (or use a microwave steamer to steam the asparagus). Steam the asparagus until tender, 4 to 5 minutes. Use tongs to transfer the asparagus to the ice-water bath, then place the spears on a kitchen towel to drain. Set the spears on a cutting board and halve on the bias.

2. In a large bowl, whisk together the lemon zest, lemon juice, miso paste, 1 teaspoon water, salt and pepper. Slowly drizzle in the oil and whisk until thick and creamy. Add the arugula, radishes and asparagus and lightly toss to combine. Transfer to a platter or individual plates and serve.