TRIM THE STEMS FROM THE BRUSSELS SPROUTS AND SLICE LENGTHWISE IN HALF.
GRATE THE ZEST FROM THE LEMON WITH A GRATER OR A MICROPLANE. SQUEEZE AND STRAIN THE LEMON JUICE INTO THE SAME BOWL.
HEAT A STEEP-SIDE FRYING PAN OR A WOK OVER MEDIUM-HIGH HEAT. POUR IN 2 TBSPS OF OLIVE OIL.
WHEN THE OIL SMOKES, ADD THE BRUSSELS SPROUTS. SALT. TOSS THE BRUSSELS SPROUTS IN THE PAN TILL THEY BROWN LIGHTLY. POUR IN ABOUT 1/2 CUP OF WATER, THE LEMON JUICE AND ZEST, AND COVER.
COOK FOR 5-8 MINUTES, DEPENDING ON THE SIZE OF THE BRUSSELS SPROUTS. WHEN THEY ARE CLOSE TO DONE, UNCOVER AND CONTINUE COOKING TILL THEY'RE TENDER AND MOST OF THE WATER HAS BOILED OFF.
REMOVE FROM THE HEAT. ADD THE BUTTER AND STIR TILL IT'S MELTED.
CHOP THE HERBS AND TOSS WITH THE BRUSSELS SPROUTS.