In a large shallow baking dish, whisk together 1 cup liquid egg whites, 1/2 cup unsweetened vanilla almond milk, 1/4 teaspoon vanilla extract, 1/4 teaspoon cinnamon, a pinch of salt, and Stevia to taste until combined.
Arrange the 4 slices of bread in the egg-white mixture and allow them to soak until they absorb the mixture, about 10–15 minutes per side.
While the bread soaks, make the powdered peanut butter filling by combining 1/4 cup PB2, 2 tablespoons unsweetened vanilla almond milk, and Stevia to taste in a bowl; stir until smooth.
Spray a large nonstick skillet or griddle with cooking spray and heat over medium.
Cook the soaked bread slices until lightly golden, about 3–4 minutes per side, working in batches if needed. Transfer cooked slices to a plate.
Assemble the stuffed French toast: spread half of the PB2 mixture on one slice, top with 1 tablespoon sugar-free strawberry jam, and place another cooked slice on top to make a sandwich; repeat with remaining slices and filling.