tortilla soup

Ingredients

• 1 large white onion,quartered
• 1-1/2 pound grape tomatoes,halved
• 2 cloves garlic,chopped
• 1/2 pound yellow summer squash,sliced
• 8 cups reduced sodium chicken broth, homemade if possible (use vegetable broth for vegetarian)
• 1 teaspoon adobo sauce from canned chipotles
• 1 large avocado,chopped
• 1/2 cup cilantro sprigs
• 3 to 4 medium yellow corn tortillas (6") sliced and crisped
• 1 medium carrot,sliced (optional)
• 1 stick celery ,sliced (optional)
• 1 package taco seasoning mix (optional)
• 4 ounces shredded cheese (cook's choice)