Cook rice in boiling salted water; drain.
Chop mushrooms; saute 2 to 3 minutes in 2 tablespoons butter.
Add stock; combine with rice.
Season to taste with salt and paprika.
Press rice mixture firmly into greased 7 inch ring mold; let stand about 5 minutes.
Turn onto a platter; keep warm.
Cook vegetable while rice is cooking.
If cauliflower is used, divide into florets.
Pile vegetable into center of mold; dot with remaining margarine.