Mix together the ancho chile powder, cumin, paprika, coriander, cayenne, garlic powder, 2 teaspoons salt and 1/2 teaspoon pepper in a small bowl. Rub the olive oil on the tenderloin, then rub evenly with the spice mixture. Let stand at room temperature for 30 minutes.
Heat the canola oil in a large ovensafe skillet, preferably cast-iron, over medium-high heat. Sear the tenderloin (bending it to fit in the skillet if necessary) until golden brown on all sides, about 3 minutes per side. Transfer the skillet to the oven and roast until an instant-read thermometer inserted into the center of the tenderloin reads 130 degrees F (for medium rare), about 20 minutes. Transfer to a cutting board and let rest for 10 minutes.
Remove the string and slice the tenderloin crosswise. Spoon over some of the Garlic-Herb Oil and sprinkle the meat with additional salt. Serve the remaining Garlic-Herb Oil in a bowl on the side.
Combine the olive oil and garlic in a small saucepan. Turn the heat to medium low and gently poach the garlic for 5 minutes; the oil should be at a very bare simmer but not boiling, otherwise the garlic will burn. Turn off the heat and allow to cool completely.
Remove the garlic from the oil and discard; transfer the oil to a bowl. Add the parsley, cilantro, chives, red pepper flakes and salt to taste to the oil and stir to combine.
The tenderloin can be transferred to a rimmed baking sheet before roasting if your skillet is not ovensafe to 450 degrees F.