Curried Coconut Green Beans

1/2 tsp black mustard seeds (opt.)
2 tsp vegetable oil
2 yellow onions, minced (about 2 cups)
1 small red onion, minced
1 1/2 tsp ground cumin
1 tsp ground coriander
1 tsp salt
1/2 tsp turmeric
1/4 ground black pepper
1/8 tsp cinnamon
1/8 tsp cayenne or 1/4 tsp red pepper flakes, or to taste
1 lb green beans, trimmed and cut into 2-inch pieces (about 3 3/4 cups)
2 TBSP mirin or 1 TBSP brown sugar
3/4 cup reduced fat coconut milk

1. If using black mustard seeds, warm the oil in a large saucepan on medium-high heat and sauté the seeds until they begin to pop. Add the onions and red onion and sauté for 5 minutes, stirring often.
2. When the onions begin to soften, stir in the cumin, coriander, salt, turmeric, black pepper, cinnamon, and cayenne, or red pepper flakes. Stir constantly for 2 minutes.
3. Add the green beans and mirin and cook for 2-3 minutes. Pour in the coconut milk, cover, bring to a simmer, and then reduce the heat to medium-low heat. Simmer until the beans are tender, about 15 minutes.
4. Serve hot.