In a large bowl, whisk eggs, milk, brown sugar, salt, vanilla, and cinnamon. Or, mix these ingredients together in a blender.
Cut the croissants in half and arrange them in a 9x13 baking dish sprayed with nonstick cooking spray in a single layer. Cut the croissants into smaller pieces to fill in any gaps, if necessary.
Pour the custard mixture over the top of the croissants.
Cover the casserole dish with plastic wrap or aluminum foil and refrigerate for at least 4 hours to overnight.
When ready to bake, remove the French toast bake from the refrigerator and allow it to sit for 30 minutes. Bake uncovered at 350 degrees for 45-50 minutes until it is a deep golden brown.
Serve with homemade caramel syrup, sliced strawberries, and whipped cream.