In a large skillet, bring the broth and butter to a boil and reduce by half. Add the zucchini and the sage or basil. Continue cooking, stirring gently, until the zucchini is just tender, 3 to 4 minutes. Season with salt and pepper. Keep warm.
In the same skillet, brown the fish in the oil over medium heat. 3 to 4 minutes per side. Season with salt and pepper.
Serve the fish topped with the pesto (see recipe) and accompanied by the zucchini.