Thoroughly combine the seasoning mix ingredients in a small bowl and set aside.
In a large heavy skillet, melt the margarine over high heat. Add the tasso and andouille if using; cook 5 minutes, stirring occasionally. Add the onions, celery, bell peppers, seasoning mix and garlic. Stir well and continue cooking until browned, about 10 to 12 minutes, stirring occasionally and scraping, the pan bottom well.
Stir in the rice and cook 5 minutes, stirring and scraping pan bottom occasionally.
Add the stock, stirring well. Bring mixture to a boil;reduce heat and simmer until rice is tender but still a bit crunchy, about 20 minutes, stirring occasionally toward the end of cooking time.
Stir in vegetables at appropriate time in order to not overcook.