Heat the olive oil in a medium size skillet. Add the onions and toss to coat. Cook for 2 - 3 minutes.
Add the kale and the garlic and continue to cook for another 5 minutes or so. The kale should be wilted and somewhat tender and the onions and garlic should be golden.
Add a little half and half to keep things moist and continue to cook until everything is very tender. Set aside
If you choose to precook the bacon, lay the strips in a medium skillet and cook over low heat 5 -7 minutes until the bacon begins to render some fat. Remove from the pan and drain on paper towels while you prepare the tenderloin.
Trim any fat from the tenderloin. Using a sharp knife, cut along the length of the tenderloin so that it lays flat. Be careful not to cut all the way through. Set aside.
Spoon the filling into the pork tenderloin stopping a bit short of the ends. Smooth the filling out stopping about 1/2 inch from the edges.
Pull the cut edges together so that the filling is completely enclosed and the tenderloin is more or less back to its original shape.
Wrap the bacon strips around the tenderloin covering it completely. Overlap the strips as necessary to create the coverage. Secure with tooth picks. Know how many you are putting in and make sure to take the same number out prior to serving.
Place the tenderloin on a preheated grill and cook over medium high heat, turning as needed to brown and cook evenly, 20 - 25 minutes. Tenderloin is done when it reaches an internal temperature of 145 degrees.
Allow the tenderloin to rest at least 5 minutes before slicing.