Brown ground beef with onion in oil in skillet, stirring until crumbly. Add next 3 ingredients, mixing well. Simmer covered, for 10 minutes. Combine biscuit mix, sour cream, egg and onion salt in bowl, stirring just until mixed. Spread very thinly over bottom and thickly over side to within 1/4 inch of top of greased and floured pie plate. Place 1/2 of the ground beef mixture in prepared pie plate, reserving remainder for future use. Bake at 400~ for 20-25 minutes or until brown. Sprinkle with cheese.