Depending on the size of your bread, roll out gently with a rolling pin to ensure each slice is large enough to fit the shape of your cookie cutter.
Use a 3-inch circular cookie/biscuit cutter to cut out DIY uncrustables shape.
Spread sunflower seed butter onto both cut-out bread circles—a thick layer on one slice, and a thinner layer on the other slice.
Mash banana and dollop onto piece of bread with the thicker layer of sunflower seed butter. Top with other bread slice and crimp edges together with a fork to seal.
(Or, you can assemble your sandwich and then use an uncrustables sandwich cutter to do the cutting & crimping all in one!)
To freeze, place all DIY uncrustables on a flat baking sheet and freeze for 2-3 hours. Once frozen, transfer into individual freezer-safe bags or containers and store in the freezer up to 2 months.
Save any excess bread and crust to use for breadcrumbs or homemade croutons—or snack on them as you prep lunch!*Nutrition provided is a best approximation, based on the above ingredient amounts and an estimate of the bread/crust cut away in the prep process!