Heat the oil in a large pan over medium heat. Mix in the tamari, and then add the tempeh. Flip the tempeh cubes around in the mixture with a spatula to coat it on all sides. Cook for about 2 minutes per side, until each side is lightly golden.
Add the onions to the pan, and continue cooking, stirring frequently, until the onion is translucent and fragrant, about 5 minutes.
Add the bell pepper, broccoli, ginger, and garlic to the pan and cook until they've softened, about 5 more minutes.
In a small bowl, whisk together the the coconut milk, vegetable stock, curry paste, salt, crushed red pepper flakes if using, black pepper. Add the mixture to the pan along with the diced mango.
Bring the mixture to a boil, and then lower the heat and allow the dish to simmer for 15 minutes, stirring occasionally.
Serve over brown rice, if using, garnished with chopped cilantro.