Preheat a sandwich press. Brush press with 1 tablespoon coconut oil.
Blend Natvia in a high-speed blender until consistency of icing sugar.
Combine 2 teaspoons of powdered Natvia and ¼ teaspoon of cinnamon a small bowl.
Place plums, cut-side down, in the sandwich press. Cook, pressing down on the lid occasionally, for 6 minutes or until plums are tender and browned. Remove plums; wipe sandwich press clean.
Meanwhile, combine remaining blended Nativa, remaining cinnamon and remaining coconut oil in a small bowl. Brush oil mixture over one side of each piece of bread.
Place four slices of bread, oiled-side down, on a board; spread with ricotta and top with plums. Top with remaining bread slices, oiled-side up. Cook in sandwich press, in two batches, for 3 minutes or until golden and heated through. Serve dusted with cinnamon mixture.