In a large saute pan, cook bison, onion, and garlic until bison is browned. Be sure to break up the pieces as you cook. Stir in salt, pepper, cumin to taste, cayenne, and tomato paste.
Stir in grains, then add 2 cups chicken stock. Bring to a light boil, then cover and reduce heat. Let simmer for about 20 minutes, stirring occasionally and adding more stock as needed to prevent sticking and allow grains to cook.
Add the greens on top and cover again. Let cook for about 5 minutes. Stir greens through the dish and serve, with balsamic vinegar drizzled over the top, if desired.