Thinly slice the steak against the grain and put in a large bowl.
Mix the hoisin sauce, soy sauce, brown sugar, vinegar, ginger, Sriracha, garlic and cornstarch in a separate bowl. Add ¼ cup of the sauce to the bowl with the steak and toss. Let marinate for 5 to 10 minutes.
Heat 1 tablespoon oil in a large skillet over medium-high heat. Add half of the bell peppers and cook, stirring, until blackened in spots, about 1 minute. Spread out on a baking sheet and repeat with another 1 tablespoon oil and the remaining peppers. Add to the baking sheet. (Spreading out the peppers prevents them from steaming.)
Add 1 tablespoon oil to the skillet. Add half of the steak in an even layer. Let cook about 20 seconds so that it starts to color, then toss and continue cooking just until the meat is no longer pink, another 30 seconds. Empty the steak onto a plate. Repeat with the remaining oil and steak.
Return the steak and peppers to the skillet and stir in the remaining sauce. Cook, tossing, until everything is well coated, about 1 minute. Serve over rice and top with scallions and cilantro.
