After steak has marinated 30 minutes, remove bowl from refrigerator and uncover. Transfer marinated steak to second large bowl and discard any remaining marinade.
Sprinkle ¼ cup cornstarch over marinated steak. Gently toss or stir steak to lightly coat all pieces with cornstarch. Set aside.
Place large skillet or wok on stovetop over medium-high heat. When pan is warm, add ¼ cup neutral oil. Continue heating pan until oil is hot and shimmery, swirling and tilting pan as needed to distribute oil across surface.
When oil is hot, place steak in skillet in one even layer, being careful not to overcrowd pan. Work in batches as needed depending on size of pan.
Pan-fry steak 2 to 3 minutes or until browned and crispy on bottom. Flip steak strips over and pan-fry on other side approximately 1 to 2 minutes or until browned, crispy, and cooked through.
Once steak is fully cooked, transfer to large plate and set aside. Repeat with any remaining slices of steak until all have been cooked through.
Drain skillet, leaving 2 tablespoons neutral oil in pan. Return pan to stovetop and reduce heat to medium.
Add 1 1-inch-long piece fresh ginger to skillet. Sauté ginger until fragrant, approximately 1 to 2 minutes, stirring occasionally to prevent sticking or burning.
When ginger is fragrant, add 2 large shallots and 4 large cloves garlic to pan. Stir to incorporate then sauté until fragrant, approximately 1 to 2 minutes, stirring occasionally.
When shallots and garlic are fragrant, add 3 medium fresno peppers. Sauté peppers 30 to 60 seconds, stirring frequently.
Add 1 small green bell pepper and 1 small red bell pepper to pan and stir to incorporate. Cook peppers 2 to 3 minutes, stirring constantly, until peppers have softened slightly.
Return steak strips to pan. Pour in prepared sauce, then add 2 scallions. Stir all ingredients together until coated in sauce, then reduce heat to medium-low and simmer mixture until sauce has been completely absorbed.