Coat a Dutch oven with cooking spray; add margarine. Place over medium-high heat until margarine melts. Add potato and next 4 ingredients; saute until crisp-tender.
Add beer and next 3 ingredients, stirring well. Bring to a boil; cover, reduce heat, and simmer 30 minutes.
Combine milk and flour, stirring until smooth. Add flour mixture to vegetable mixture. Cook over medium heat, stirring constantly, until mixture is thickened and bubbly. Add cheese and parsley, stirring until cheese melts. To serve, ladle soup into individual bowls, and serve with Peppered Toast Triangles.