Bring a large pot of water to a boil. Blanch beans until tender, about 6 minutes. Drain.
Meanwhile, heat 1 1/2 teaspoons oil in
a large nonstick skillet over medium heat.
Cook shallots, stirring occasionally, until
tender and just starting to brown, 3 to
4 minutes. Transfer shallots to a small bowl,
and wipe skillet clean with a paper towel.
Whisk together stock and cornstarch. Heat remaining tablespoon oil in skillet over high heat. Cook mushrooms, stirring occasionally, until golden brown, about 6 minutes. Reduce heat to low; add shallots. Whisk in stock mixture. Cook until thick, about 3 minutes more. Remove from heat. Stir in yogurt and 1/2 teaspoon salt; season with pepper. Toss in beans. Serve warm.