In greased 8X12 inch pan, combine first four ingredients and one cup of cheese. Blend soup and 3/4 c. milk; pour over casserole. Bake, covered at 400 degree oven for 15 minutes. Prepare biscuit mix, milk and 1/2 can of onions; mix thoroughly. Drop by spoonfuls to form 6 biscuits around the edge of casserole. Bake, uncovered for 15 to 20 minutes, or until biscuits are golden brown. Top with remaining onions and cheese and bake another 2 to 3 minutes, until onions are toasted.