Combine ½ cup allulose and the arrowroot powder or corn starch in a food processor or blender and process until it becomes a fine dust.
Crumble a piece of parchment paper big enough to overhang the pan at the edges and line a 9-inch square cake pan with it. Grease the paper with coconut oil. Dust with some of the allulose dust.
Put ½ cup water in the bowl of an electric mixer fitted with the whisk attachment. Sprinkle the gelatin over the water, stir, and let sit while preparing the rest.
Combine the remaining ¾ cup water and 3 cups allulose in a deep saucepan. Stir to combine them and bring to a boil. Do not stir anymore once the allulose has dissolved. Boil until the mixture reaches 240°F on a candy thermometer.
Turn the mixer on low and carefully pour in the hot allulose mixture. Add the salt. Once the mixture is very foamy, turn the speed up to high and beat for 15 minutes or until it turns into a very white fluffy mass. Beat in the vanilla.
While the marshmallows are mixing, put the strawberries in a sealable bag and roll with a rolling pin until they become strawberry dust. When the marshmallows are done mixing, turn the mixer to low and slowly add the crushed strawberries. Using a rubber spatula, mix until fully combined and not streaky. Put the mixture into the prepared pan and smooth the top. Let sit, uncovered, at room temperature for at least 8 hours.
Sprinkle some of the allulose dust over the top of the marshmallows and on a flat work surface. Using the parchment, transfer the marshmallows to the work surface and cut with a sharp, thin, oiled knife into 1-inch squares, rolling them in more of the allulose dust to keep from being too sticky.
Melt the chocolate and coconut oil together and let cool.
Place some waxed or parchment paper on a baking sheet and then put a cooling rack on top. Place the cut marshmallows on the rack and spoon chocolate over the top, letting some drip -down.