How to keep saute pan hot without it burning for searing fresh greenbeans or zucchini

Im working in a restaurant that has pan-seared greenbeans and sauted chopped zucchini with onions&peppers. It seems were constantly waiting for the damned veggies or GB to complete our plates so the rest of the meal gets effing' cold! After a few batches the pan gets all charcoaly and the veggies get all grainy and ugly. (We use nonstick spray to do the greenbeans and in a separate saute pan we use a soysauce type mix for the zucchini stuff.)