Remove ends from beans and cut into bite-size pieces.
Place beans in 1 inch of water in saucepan. Bring to a boil and cook beans uncovered for 5 minutes. Cover pan and cook until beans are tender, about 7 minutes. Drain beans and set aside. Keep warm.
Cook shallots and mushrooms in olive oil for 4 minutes. Sprinkle with garlic salt and black pepper. Add with tomatoes to green beans and mix.