Saute onions in a couple tablespoons of butter. Add rice/lentils. Season with salt and pepper.
Cut off the tops of 4-6 medium tomatoes and gut the inside - reserving all the parts for later use.
Chop up the tomato guts. Mix with 1 tbs olive oil and a crushed clove of garlic. Place tomatoes in a greased baking dish. Fill tomatoes with lentil/rice mixture, drizzle some of the tomato gut mixture over the top. Put the top of the tomato back on.