Turkish-Style Braised Green Beans

In a large sauté pan or heavy pot, heat the oil over medium-high heat until hot but not smoking. Add the onions and stir occasionally, until softened, about 5 minutes. Add the garlic and continue to cook, stirring frequently, 2 minutes.
Add the beans, tomatoes, 1 cup water, sugar, salt and pepper and bring just to a boil. Reduce heat to low, then cover and simmer until the beans are very tender, about 45 minutes.
Remove from heat, adjust the seasoning to taste and cool to room temperature, uncovered, about 45 minutes. Stir in the mint and serve, with thick yogurt and lemon wedges.