Start by preparing the vol-au-vent. Since it takes only a couple of minutes to heat up, put it in the oven when the sauce is almost done. Put aluminum on a baking sheet and place the vol-au-vents on the pan. Make sure that you removed the round center "cap" part of the shells. you can use a butter knife or a spoon to gently cut it out and place them next to the shells on the baking pan.
Make the béchamel sauce. In a medium saucepan, melt butter on medium heat and put the bay leaf and the garlic, cooking for 30 seconds and add the flour and let it cook another 30-60 seconds, whisking, and be sure not to burn it. Gradually add the milk, by pouring 1/4 cup at a time, waiting until it thickens up a little bit and then add more milk. Continue to whisk and get red of the lumps, add the salt and pepper to taste and cook until you get the desired consistency. Add in the frozen peas.
Remove from the stove top and add the cooked diced chicken breast in the sauce, spoon over the warm vol-au-vent shells and enjoy!