Place tomatoes in container of an electric blender; process until pureed. Combine tomatoes, onion, and salt in a saucepan; bring to a boil . Reduce heat; simmer 5 minutes or until onion is tender.
Cut tortillas into fourths; fry in 1/4 inch hot oil 5 seconds on each side or until softened and lightly browned. Drain well.
Layer one-third of tortillas in a lightly greased 2-quart casserole. Layer half of tomato mixture, diced pork, sour cream, green chiles, and cheese over tortillas. Repeat procedure.
Cover and bake at 350° for 10 minutes. Place remaining tortillas around outside edge of casserole. Bake, uncovered, an additional 10 minutes. Garnish with hot pepper slices. Serve immediately.