Applebee's Cheese Chicken Tortilla Soup

Source: Applebee's

1 medium yellow onion, chopped (1 cup)
2 teaspoons fresh garlic, minced
2 tablespoons vegetable oil
4 cups chicken stock
1/4 cup chopped green pepper (optional)
1 (15 ounce) can tomato puree
1 tablespoon finely minced jalape