Tuna, Mushroom, Mixed Veggies Rice Topping

This is a modified tuna casserole recipe. Instead of mixing it with noodles, I used it as topping on rice.

1 can cream of mushroom soup
1 can tuna, drained
half an onion
1 C mixed vegetables, prepared
ground black pepper
5 slices of cheese

Over medium heat, mix everything in a pan, stirring constantly until the cheese melts.