In a small saucepan over low heat, melt butter and chopped chocolate, whisking until smooth.
Add cacao powder, and whisk again until it is smooth with no lumps. Remove from heat and set aside.
In a large bowl, whisk together the eggs, Swerve, Yacon syrup, liquid stevia, & salt. Add chocolate-butter mixture and vanilla & whisk until smooth.
Pour the mixture into the prebaked crust. It will not come all the way to the top. This is fine, it will rise as you add the pecans.
Arrange pecans nice side facing up, over the chocolate filling in one layer. Then add another layer on top. You may lightly press the pecans down into the chocolate filling, so that all the pecans are nestled into the filling, but not submerged.
Transfer the pie to a large rimmed baking sheet to catch any spills, and bake until the filling is set about 30 minutes. It is done if when you jiggle the pan the filling doesn't move too much, but a little bit is ok okay. If it shakes a lot, cover your pie loosely with foil and bake for an additional 10-20 minutes or until just barely jiggly. The filling will continue to set as it cools.
Note: while baking, the filling may crack & puff up a bit, but it will lay back down as it cools. If you don't want your pie to crack then bake your pie with an ovenproof casserole dish filled with hot water on the bottom oven rack, which will keep it from cracking.
Remove the pie from the oven and allow to cool completely on a wire rack 2-3 hours or overnight, before serving.
Cut into 12 slices.