Line a small baking sheet with parchment paper. Slit each date lengthwise with a paring knife and pull out the pit, keeping the date intact like a pocket.
Spoon about 2 teaspoons peanut butter into each date, then pinch the sides gently to close. Set the filled dates on the lined sheet.
Put the chopped chocolate and coconut oil in a microwave-safe bowl. Microwave 30 seconds, stir, then microwave in 15-second bursts, stirring between each, until smooth, about 1 minute total.
Dip each date halfway into the chocolate, let the excess drip back into the bowl, and return it to the sheet. Sprinkle with peanuts and flaky salt while the chocolate is still wet.
Refrigerate 20 minutes, until the chocolate is set. Store airtight in the fridge up to 5 days and let the dates sit at room temperature for 10 minutes before serving.