Vegetarian Chili

1 1/2 cups chopped yellow onion s

1 cup chopped red bell pepper s

2 tablespoons minced garlic

2 to 3 serrano pepper s, stemmed, seeded, and minced, depending upon taste

1 medium zucchini , stem ends trimmed and cut into small dice

2 cups fresh corn kernels (about 3 ears)

1 1/2 pounds portobello mushroom s (about 5 large), stemmed, wiped clean and cubed

2 tablespoons chili powder

1 tablespooon ground cumin

1 1/4 teaspoons salt

1/4 teaspoon cayenne

4 large tomato es, peeled, seeded and chopped

3 cups cooked black bean s, or canned beans, rinsed and drained

1 (15-ounce) can tomato sauce

1 cup vegetable stock , or water

1/4 cup chopped fresh cilantro leaves

Sour cream , garnish

Diced avocado , garnish

Chopped green onion s, garnish

Shredded cheddar cheese, garnish