Preheat oven to 350°F (175°C).

In a bowl, combine ground beef and chopped onion.

In a separate small bowl, mix together salt, pepper, chili powder, and flour.

Butter a 3-quart casserole dish.

Place the instant rice in the buttered casserole dish, followed by 1/3 of the flour mixture.

Add a layer of the ground beef and onion mixture.

Pat about 1/3 of the flour mixture on top of the beef layer.

Dot with margarine (or butter).

Pour in the canned tomatoes and sprinkle another 1/3 of the flour mixture on top.

Dot with margarine (or butter).

Add the canned corn, including the liquid, as the last layer.

Dot with margarine (or butter).

Bake in the preheated oven for approximately 1 hour, or until bubbly and cooked through.