Heat up the vegetables in a bowl (or the steamer bag) in the microwave according to the directions on the package.
Place the rice in a glass or ceramic baking dish you can just plop it in there and kind of evenly spread it out.
In a saucepan on the stove melt the butter and fry up the onions until they start getting a little color.
Stir in flour until thoroughly incorporated then whisk in stock and cream.
Dump in the mustard and cheese at this point and season with salt and pepper.
Dump the veggies in the cheese mixture and give it a little stir.
Dump your cheese-vegetable mix on top of the rice. Put the whole thing in the oven at 350 for about 10 minutes just for one last heat through.