1. Melt half the margarine in an ovenproof saucepan / casserole dish.
Add oats, oatmeal and nuts and cook for 3 minutes.
Put in bowl.
2. Chop carrot, mushrooms onion and kidney beans finely (food processor very handy here!).
Melt rest of margarine, add chopped vegetables, and cook for another 2 minutes.
Add the rest of the ingredients, and the oat mixture.
Cook for 5 minutes.
3. Transfer to medium oven for 40 minutes.
Traditionally, serve with "bashed neeps" (mashed swede) and "mashed tatties" (mashed potatoes) and copious amounts of whiskey.
Also goes well with roast onions (put in the oven 10 minutes before the haggis). (The fat content can be reduced by halving (or removing) the suet. If this is done, check it isn't getting too dry, and add some veggie stock if necessary.)
Source: Various web pages that seem to have copied off of each other.