Heat a wok or cast-iron skillet on high heat until lightly smoking. Add the ginger slices and char on both sides until slightly blackened, about 4 minutes. Remove the ginger from the pan and mince it. Combine ginger with the next five ingredients, then whisk or blend thoroughly.

Add the oil to the pan (carefully, if it's still hot), and heat on high until simmering. Add the green beans and stir briefly to coat in the oil, then let them sit for a minute or two to brown. Continue to toss every minute or so to let new beans blacken against the hot surface of the pan, until most of the beans have dark spots and the remainder are still bright green - approximately 6-8 minutes.

Remove beans from heat, transfer to a serving bowl, and toss with the sauce. Serve on its own, or over noodles or rice.