Upside-Down Tamale Pie

For meat filling: 

2 tablespoons extra-virgin olive oil or vegetable oil

1 1/2 cups chopped fresh or frozen onions (2 medium yellow onions)

1 large garlic clove, minced

Half of a 1-pound bag frozen bell pepper stir-fry mix (red, green, and yellow peppers; do not thaw)

2 teaspoons chili powder

1 teaspoon dried oregano, crumbled

1 pound lean ground beef chuck

3 tablespoons all-purpose flour

One 1-pound jar chunky salsa (as mild or hot as you like)

2 tablespoons tomato paste

One 9-ounce package frozen whole-kernel corn (do not thaw)

Salt and freshly ground black pepper

2 tablespoons coarsely chopped fresh cilantro or parsley

For corn bread topping:

1 cup all-purpose flour

3/4 cup yellow cornmeal 

2 tablespoons freshly grated Parmesan cheese 

2 teaspoons baking powder 

1 teaspoon baking soda 

1 teaspoon salt 

1 teaspoon chili powder 

1 teaspoon dried oregano, crumbled 

1/4 teaspoon freshly ground black pepper 

1 cup buttermilk 

1/4 cup extra-virgin olive oil or vegetable oil 

1 extra-large egg