Heat the fat in a medium-size saucepan over high heat until very hot but not quite smoking. Add the onion and garlic and cook, stirring occasionally, for 2 minutes. Reduce the heat to medium and cook, stirring, another 3 minutes, or until the onion starts to color. Add the poblanos and epazote or cilantro and stir to combine. Cook, stirring occasionally, for another 5 minutes.