(Make sure you have rice cooked for serving!)
In a large skillet over medium heat, add the oil, white/light green parts of scallion, and ½ teaspoon salt. Cook for 3 minutes, or until softened, stirring occasionally.
Add the beans, water, and ½ teaspoon salt and simmer over medium/medium-low heat for about 5 minutes or until the water has reduced a bit. Tilt the pan to remove some of the water (about ¼ cup), transfer to a small bowl, and mash it up with the miso paste into a smooth paste.
Turn off the heat and add miso back to the pan along with the butter and stir everything together until smooth and butter has melted. You can also stir in some of those dark green scallions here, but save some for topping as well.
In a medium bowl, add beets, lemon, and remaining ½ teaspoon salt and toss to coat.
Serve the miso butter beans over warm rice and top with the lemony beets (get that tangy beet liquid on there too!), dark green parts of the scallions, sesame seeds (if using), and squeeze of lemon.