Heat a large Carbon Steel Frying Pan or Griddle over medium-high heat until hot.

Toss poblanos in 1 Tbsp. oil and cook until all sides have color and start to blister, 10–12 minutes. Place in a medium bowl and cover with plastic to steam, about 8 minutes.

Meanwhile, using a Chef Knife, slice onions in half lengthwise and then lengthwise again into ¼-inch-thick slices. Toss with remaining 1 Tbsp. oil, salt, and pepper and cook, stirring, until browned, 6-7 minutes.

Peel poblanos and cut into ¼-inch strips. Once onions have a little bit of color, add poblano strips to griddle and mix well. Use some of the poblano steaming liquid to deglaze griddle. Once everything is incorporated, remove rajas and reserve. Chill until ready to assemble.