Saute onion and garlic in 1/2 tablespoon hot oil until translucent. Remove from heat and let cool. Mix with ricotta cheese. Season with salt and pepper. Spoon this mixture into the canneloni noodles and place noodles in a buttered casserole dish. To make sauce, saute garlic in 1 tablespoon olive oil until just brown. Add both cans of tomatoes with liquid and let simmer. Season with salt and pepper. Pour sauce on filled canneloni. Sprinkle with Parmesan and dot with butter. Bake in preheated 400 degrees F oven for 25 minutes.