In a small bowl, stir together the soy sauce, miso, sesame oil and rice vinegar to make a thick sauce.
In a large skillet, heat 1 tablespoons of peanut oil over medium high heat. Add the asparagus and a pinch of salt and cook, stirring often, until bright green and just beginning to soften. This will take about 2-3 minutes, depending on the thickness of your asparagus.
If the skillet seems dry, add the other tablespoon of peanut oil. Reduce heat to medium and add the garlic. Cook for about a minute, stirring often so garlic is well distributed and doesn't burn.
Remove skillet from heat and pour over miso sauce mixture. Stir for another minute or so, just until the sauce is warmed through and coats the asparagus.
Serve immediately, garnished with sesame seeds if desired.