First make the pickle. Pack the radish sticks and cucumbers into a jar, along with the cilantro. Heat the vinegar, water, and pepper flakes to a boil on the stove or in the microwave. Pour the hot brine over the vegetables, the liquid should just cover them. Set aside.
Whisk the dressing ingredients together, taste to adjust any of them, and set aside.
Cook the rice according to package instructions. Toss it with the seaweed and some of the dressing to moisten and flavor it.
Divide the rice between two bowls. Place the tuna in each bowl. Lift the tuna out gently with a fork to keep the chunks intact and leaving most of the oil in the can.
Arrange the rest of the ingredients around the bowl and drizzle with the dressing. Top with garnishes, and serve.
Notes
You can find pickled ginger in jars in the Asian section of your supermarket.
Sesame oil is one of my favorite ingredients, but it's intensely flavored, and expensive. If you like you can cut it down with any mild oil you like, avocado, almond, or even canola oil would work. If you want to use olive oil, make sure you use mild flavored pure oil, not extra virgin.
Traditional poke bowls are served with warm rice and cold toppings. I found that cold rice worked, too. In either case toss the rice with some of the dressing for flavor.
Other poke bowl toppings you might try would be avocados, green onion, pineapple, papaya, jicama, bell peppers, Maui onion, or edamame beans.