Heat oven to 400°F. (This recipe could also be made in a toaster oven or air fryer.)
Using the back of a spoon, or your fingers, gently smoosh each slice of bread to create a depression, leaving the edges unsmooshed to contain the custard.
In a small bowl, whisk together the egg, yogurt, sweetener, and, if using, the vanilla bean paste.
Divide the custard equally between the two slices of bread and top with strawberries slices, or the toppings of your choice.
Bake for 10 to 12 minutes, or until the custard is set.