Fill a bowl halfway with cold water and add some ice cubes to make an ice bath. Bring a small pot of generously salted water to a boil over high heat. Add the peas and cook until just tender, 30 seconds. Transfer them to the ice water to stop the cooking process. Drain.
Combine the rice and 6 cups cold water in a pot. Sprinkle in 2 teaspoons salt and bring to a boil over medium-high heat. When the water comes to a boil, reduce the heat to low and cover. Cook the rice without peaking under the lid -- the steam is most precious in cooking rice -- for 20 minutes.
Let the rice sit off the heat, undisturbed and with the lid on, for at least 5 minutes. This allows the rice to steam, and makes the bottom layer as fluffy as the top.
Fluff the rice with a fork and transfer to a serving bowl. Add the peas, green onions, lemon zest and juice, mint and olive oil; season with some salt and pepper. Toss gently, taking care not to smash the grains of rice. Garnish with pea tendrils, if using, and serve.