In a small food processor, puree the banana, peanut butter, 2 tsp. coconut oil and vanilla extract until smooth and creamy. Set aside.
Place the chocolate and 2 tbsp coconut oil into a medium sized glass bowl and set it over a small sauce pot filled 1 inch up with water. Bring the water to a simmer and slowly stir the chocolate until it melts. Remove from the heat.
Using a small spoon, carefully spoon a thin layer of dark chocolate onto the bottoms of 8 regular sized silicon muffin containers or 50 very mini sized silicon molds. Place the molds onto a baking sheet and transfer to the freezer to harden for at least 5 minutes.
Once set, make a ball no wider than the diameter of the muffin or candy mold and press it on top of the chocolate base, being careful not to touch the sides of the mold but also to try to make as flat a surface as possible. If using a regular sized mold, I recommend a heaping tablespoon of filling, and if using the mini candy molds, more like ½ teaspoon.
Using a small spoon, very gingerly pour the chocolate down the sides to envelope the filling and on the top to fully cover the peanut butter. Transfer to the freezer to fully set- at least 20 minutes.
These can be made well in advance, but are best enjoyed within 15 minutes of removing them from the freezer.