How to Make It
Light a grill or preheat a grill pan. Lightly rub the chiles with oil and grill over high heat, turning occasionally, until lightly charred all over. Transfer the chiles to a bowl and cover with a towel. Let the chiles cool.
Wearing latex gloves, rub the skins off of the chiles then remove the stems and seeds. Halve the smaller chiles and cut the larger ones into 1/2-inch strips. Pat the chiles dry.
Transfer the chiles to small resealable freezer bags, storing the mild ones (like poblanos and Anaheims) separately from the hot ones (like Fresnos, jalapeños, serranos and habaneros). Sprinkle them very lightly with oregano. Add enough oil to cover the chiles. Seal the bags, pressing out the air, and freeze for up to 6 months.