With the rack in the middle position, preheat the oven to 450°F (230°C). Line a baking sheet with aluminum foil.
In a non-stick skillet over medium-high heat, soften the vegetables in the butter for 5 minutes. Sprinkle with the flour and cook for 1 minute, stirring constantly. Add the milk and broth. Bring to a boil while stirring. Add the chicken. Simmer for 10 minutes, stirring occasionally, until the béchamel sauce thickens and the vegetables are tender. Add the peas. Season with salt and pepper.
Place the baguette halves side by side on the baking sheet, cut side up. Cover with the chicken mixture and bake for 8 minutes. If desired, finish under the broiler for 2 to 3 minutes until golden brown.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.