1. Adjust oven rack to lower-middle position and heat oven to 275°F. Heat oil in Dutch oven over medium heat until shimmering. Add onion and cook, stirring occasionally, until softened, 3 to 5 minutes. Add garlic, allspice, and cayenne; cook until fragrant, about 30 seconds. Add water, baking soda, and green beans and bring to simmer. Reduce heat to medium-low and cook, stirring occasionally, for 10 minutes. Stir in tomato paste, tomatoes and their juice, salt, and pepper.

2. Cover pot, transfer to oven, and cook until sauce is slightly thickened and green beans can be easily cut with side of fork, 40 to 50 minutes. Stir in mint and season with vinegar to taste. Sprinkle with feta and serve warm or at room temperature.

Serves 4 to 6 as a side dish