Melt 2 tablespoons of the butter in a large skillet over medium-high heat. Add the bread cubes and cook for 8 minutes or until toasted on all sides, stirring frequently. Remove the bread cubes to a platter, reserving the pan drippings.
Melt the remaining 4 tablespoons butter with the reserved pan drippings over medium–high heat and add the mushrooms and green onion. Sauté for 8 minutes or until the mushrooms are tender. Add the shrimp and cook for 3 minutes or until the shrimp turn pink. Stir in the sherry and lemon juice and cook for 1 minute. Remove from the heat and season to taste with salt and pepper. Add the bread cubes and toss to combine. Serve immediately.